Blavatsky on the subject of karma:

Is [karma] an intelligent law?

For the Materialist, who calls the law of periodicity which regulates the marshalling of the several bodies, and all the other laws in nature, blind forces and mechanical laws, no doubt Karma would be a law of chance and no more. For us, no adjective or qualification could describe that which is impersonal and no entity, but a universal operative law. If you question me about the causative intelligence in it, I must answer you I do not know. But if you ask me to define its effects and tell you what these are in our belief, I may say that the experience of thousands of ages has shown us that they are absolute and unerring equity, wisdom, and intelligence. For Karma in its effects is an unfailing redresser of human injustice, and of all the failures of nature; a stern adjuster of wrongs; a retributive law which rewards and punishes with equal impartiality. It is, in the strictest sense, "no respecter of persons," though, on the other hand, it can neither be propitiated, nor turned aside by prayer. This is a belief common to Hindus and Buddhists, who both believe in Karma.

Karma creates nothing, nor does it design. It is man who plans and creates causes, and Karmic law adjusts the effects; which adjustment is not an act, but universal harmony, tending ever to resume it original position, like a bough, which, bent down too forcibly, rebounds with corresponding vigor.

Sometimes the law of karma (or action) seems too abstract. Here a short passage showing that our low thoughts & feelings have an effect now, in this lifetime. This quote is from some unknown Pt. Loma theosophist, who was writing around 1907.
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The morphine and opium dens only provide method and opportunity of indulgence for the increasing numbers who desire to reduce their souls to stagnation with that drug. So with the drink stores and the drink habit. Going one layer deeper, we can say that the morphinomaniac, the dipsomaniac, the elemental sub-human criminals and roues are only the focal units in the general human consciousness to which converge and where accumulate the tendencies to those things existing in many men. Five per cent of vicious (though possibly checked) thought in twenty men cause a whole vicious act in the twenty-first. Him alone do we punish; but in passing we might ask, is there not a Law and insight deeper than human which will apportion to the twenty their share of punishment? Prisons, Reformatories, Lunatic Asylums, the graves of suicides, opium dens and inebriate Homes, are filled with the integrated results of these unnoticed `five-per-cents' in you and me.

While it is encouraging to know that the noblest & best parts of our inner life are, at times, definitely helping some of our fellows; it is also sobering to think of the responsibility we incur, when some of our vileness corrupts another into doing evil. Who wants to contribute the "last straw" that breaks the spiritual backbone of a staggering, overloaded pilgrim soul?

Aphorisms on Karma

The following, among others not yet used, were given to me by teachers, among them being H. P. Blavatsky. Some were written, others communicated in other ways. To me they were declared to be from manuscripts not now accessible to the general public. Each one was submitted for my judgment and reason; and just as they, aside from any authority, approved themselves to my reason after serious consideration of them, so I hope they will gain the approval of those my fellow workers to whom I now publish them. -- William Q. Judge

(1) There is no Karma unless there is a being to make it or feel its effects.

(2) Karma is the adjustment of effects flowing from causes, during which the being upon whom and through whom that adjustment is effected experiences pain or pleasure.

(3) Karma is an undeviating and unerring tendency in the Universe to restore equilibrium, and it operates incessantly.

(4) The apparent stoppage of this restoration to equilibrium is due to the necessary adjustment of disturbance at some other spot, place, or focus which is visible only to the Yogi, to the Sage, or the perfect Seer: there is therefore no stoppage, but only a hiding from view.

(5) Karma operates on all things and beings from the minutest conceivable atom up to Brahma. Proceeding in the three worlds of men, gods, and the elemental beings, no spot in the manifested universe is exempt from its sway.

(6) Karma is not subject to time, and therefore he who knows what is the ultimate division of time in this Universe knows Karma.

(7) For all other men Karma is in its essential nature unknown and unknowable.

(8) But its action may be known by calculation from cause to effect; and this calculation is possible because the effect is wrapped up in and is not succedent to the cause.

(9) The Karma of this earth is the combination of the acts and thoughts of all beings of every grade which were concerned in the preceding Manvantara or evolutionary stream from which ours flows.

(10) And as those beings include Lords of Power and Holy Men, as well as weak and wicked ones, the period of the earth's duration is greater than that of any entity or race upon it.

(11) Because the Karma of this earth and its races began in a past too far back for human minds to reach, an inquiry into its beginning is useless and profitless.

(12) Karmic causes already set in motion must be allowed to sweep on until exhausted, but this permits no man to refuse to help his fellows and every sentient being.

(13) The effects may be counteracted or mitigated by the thoughts and acts of oneself or of another, and then the resulting effects represent the combination and interaction of the whole number of causes involved in producing the effects.

(14) In the life of worlds, races, nations, and individuals, Karma cannot act unless there is an appropriate instrument provided for its action.

(15) And until such appropriate instrument is found, that Karma related to it remains unexpended.

(16) While a man is experiencing Karma in the instrument provided, his other unexpended Karma is not exhausted through other beings or means, but is held reserved for future operation; and lapse of time during which no operation of that Karma is felt causes no deterioration in its force or change in its nature.

(17) The appropriateness of an instrument for the operation of Karma consists in the exact connection and relation of the Karma with the body, mind, intellectual and psychical nature acquired for use by the Ego in any life.

(18) Every instrument used by any Ego in any life is appropriate to the Karma operating through it.

(19) Changes may occur in the instrument during one life so as to make it appropriate for a new class of Karma, and this may take place in two ways: (a) through intensity of thought and the power of a vow, and (b ) through natural alterations due to complete exhaustion of old causes.

(20) As body and mind and soul have each a power of independent action, any one of these may exhaust, independently of others, some Karmic causes more remote from or nearer to the time of their inception than those operating though other channels.

(21) Karma is both merciful and just. Mercy and Justice are only opposite poles of a single whole; and Mercy without Justice is not possible in the operations of Karma. That which man calls Mercy and Justice is defective, errant, and impure.

(22) Karma may be of three sorts (a) Presently operative in this life through the appropriate instruments; (b ) that which is being made or stored up to be exhausted in the future; ( c) Karma held over from past life or lives and not operating yet because inhibited by inappropriateness of the instrument in use by the Ego, or by the force of Karma now operating.

(23) Three fields of operation are used in each being by Karma: (a) the body and the circumstances; (b ) the mind and intellect; ( c) the psychic and astral planes.

(24) Held-over Karma or present Karma may each, or both at once, operate in all of the three fields of Karmic operation at once, or in either of those fields a different class of Karma from that using the others may operate at the same time.

(25) Birth into any sort of body and to obtain the fruits of any sort of Karma is due to the preponderance of the line of Karmic tendency.

(26) The sway of Karmic tendency will influence the incarnation of an Ego, or any family of Egos, for three lives at least, when measures of repression, elimination, or counteraction are not adopted.

(27) Measures taken by an Ego to repress tendency, eliminate defects, and to counteract by setting up different causes, will alter the sway of Karmic tendency and shorten its influence in accordance with the strength or weakness of the efforts expended in carrying out the measures adopted.

(28) No man but a sage or true seer can judge another's Karma. Hence while each receives his deserts appearances may deceive, and birth into poverty or heavy trial may not be punishment for bad Karma, for Egos continually incarnate into poor surroundings where they experience difficulties and trials which are for the discipline of the Ego and result in strength, fortitude, and sympathy.

(29) Race-Karma influences each unit in the race through the law of Distribution. National Karma operates on the members of the nation by the same law more concentrated. Family Karma governs only with a nation where families have been kept pure and distinct; for in any nation where there is a mixture of family -- as obtains in each Kaliyuga period -- family Karma is in general distributed over a nation. But even at such periods some families remain coherent for long periods, and then the members feel the sway of family Karma. The word "family" may include several smaller families.

(30) Karma operates to produce cataclysms of nature by concatenation through the mental and astral planes of being. A cataclysm may be traced to an immediate physical cause such as internal fire and atmospheric disturbance, but these have been brought on by the disturbance created through the dynamic power of human thought.

(31) Egos who have no Karmic connection with a portion of the globe where a cataclysm is coming on are kept without the latter's operation in two ways: (a) by repulsion acting on their inner nature, and (b ) by being called and warned by those who watch the progress of the world.

You can do nothing better than to study the two doctrines -- of Karma and Nirvana -- as profoundly as you can. Unless you are thoroughly well acquainted with the two tenets -- the double key to the metaphysics of Abidharma -- you will always find yourself at sea in trying to comprehend the rest. We have several sorts of Karma and Nirvana in their various applications -- to the Universe, the world, Devas, Buddhas, Bodhisatwas, men and animals -- the second including its seven kingdoms. Karma and Nirvana are but two of the seven great MYSTERIES of Buddhist metaphysics...

Mahatma letter 16

From Theosophia, Fall 1963:

KARMA - MAN’S PERENNIAL OPPORTUNITY
Montague A. Machell

It is the contention of many an orthodox devotee that God never closes a door without opening a window, a contention more sound than even the most orthodox may realize. Its complete dependability, when freed of the limitations inseparable from the dogma of a personalized deity, inheres in a far broader concept: i.e., the perfect justice of Universal Law, of which this world is a manifestation.

Once propound the idea that a mortal, whose destiny is spiritual growth, comes into incarnation with the Will to Growth, in the deepest heart of him, and it must follow that this earth, his Field of Growth, is primordially endowed with the climate and opportunities for such Growth - or Universal Law is a figment of the imagination.

But before the dependability of Universal Law can become completely convincing, its own limitless universality must find application, to the life of man in a human Time Plan correspondingly limitless. Such a Time Plan makes the generally accepted 75-year, one-life program of man on earth totally irrelevant. Universal Law can only find logical application to a Universal Man - a man who in his deepest nature is Timeless and Immortal, with an Immortal Destiny.

Research into the wisdom of earliest antiquity reveals the fact that the most enlightened teachers of every age have been of this opinion and have preached a limitless Time Plan for the realization of man’s spiritual potentialities. They based this Time Plan on the perfectly logical program of not just one, but a splendid succession of incarnations upon earth, designed to allow uninterrupted progress for the incarnating Self along the pathway to ultimate Spiritual Enlightenment, the destined Maturity of a Spiritual Being.

Likewise, in harmony with the perfect operation of Universal Law, the - Ancient Wisdom makes the slowly maturing Pilgrim responsible for his own actions, each of which is necessarily governed by the undeviating law of Cause and Effect. It implies, rather reasonably, that he who plants roses on earth may count on reaping them; he who plants weeds may depend upon it that his harvest will be - weeds. And, since life’s primary purpose is the undisturbed acquirement of ever deeper wisdom, no special arrangement of any kind is permitted to interfere with the harvest, be it roses or weeds. Man learns by doing - given sufficient time!

The wise men of India applied to the personal harvest of each man’s personal sowing the term “Karma,” maintaining, with a later Teacher, that “As ye sow so shall ye also reap.” But they did not add “unless ...” with an appended “escape clause,” because, after all, as these Wise Ones saw it, Life is not primarily a question of Sin and Salvation; it is a program of Growth in Wisdom; and man grows wise from making mistakes, recognizing them as mistakes, and profiting by the lesson learned.

Their approach to this program shunned the rather prevalent orthodox view of man as innately sinful. Instead, the Wisdom Religion seeks to nourish the Spiritual Self of man with a vision or ever-expanding fulfillment of a sublime destiny - GROWTH in excelsis!

It is hardly necessary to labor the point that the prevalent mood in much of human life today is one of Disappointment. Very rarely does one encounter a person in whom inner fulfillment finds expression in a cheerful serenity. Even great material success seems to exercise a haunting influence on many, whether it spring from unsatisfied hunger for yet larger success, or a gnawing fear that this success may be swept away. Wherever one turns, he encounters again and again the spectre of insecurity. In an age of multiplying conveniences, indulgences and distractions, the justification for feelings of insecurity, inadequacy or disappointment would seem to be wholly lacking.

Could these feelings, by any chance, even in the materially successful man, betray the suspicion of an actual, though unconfessed, inadequacy in the life he is living? Impossible as it might be to convince the dissatisfied millionaire that he is the victim of a very real inadequacy, such would be the diagnosis of anyone versed in the truths of Theosophy. Such a one might further point out that this disappointment is the inevitable Karma of him who works merely for self. Should the patient have the honesty and courage to accept such a diagnosis, the Karma of its acceptance could well be a freedom and serenity of mind never before conceived as attainable. In this instance the fruit of the seed of inner faith takes the form of a sweet and nutritious self-confidence. The seemingly cruel Karma of insecurity and anxiety reveals itself as the warning that made possible this fruitful and serene living - one small example of Karma as a priceless incentive to Growth: Man closes a door on the Hall of Selfish Living; Karma opens a window on the fragrant fields of Spiritual Unfoldment; inadequacy of the personal man yields place to the Confidence of an inborn Will to Growth.

But let us not confuse the insecure millionaire with the serene seeker for Truth. The first is a stronger to his innermost Reality; the second has turned his back on the treacherous mirage of material success and has dared to contemplate the eternal roots of Godhood within himself. “This,” to borrow a popular expression, “is where he came in” - the divinely endowed Pilgrim entering the path of earthly probation, his inborn Godhood his sole capital in hand. Because that “capital” is his own holiest essence, time, events, people, cannot touch it. Karma, carried over from past incarnations, will put to the test again and again the integrity, endurance and purity of his innate divinity, in whose radiance each smallest Karmic residue can become the raw material of new revelations in wisdom and self-realization. The outcome, in every instance, must be governed by the disciple’s relation to life.

Pledged to Reality, fearing nothing, every Karmic test can prove a cherished opportunity to extract the very essence from an experience some former personality had cast aside unused. Having advanced some few small steps along the way of Selfless Living, what in some former life might have amounted to a reluctant “squaring of accounts” reveals itself here as an opportunity to build understandingly hope and confidence in a disheartened fellow-pilgrim. In the light of Reality, one gives one’s life out of sheer gratitude for this glowing Gift of Life. One reaches out to the unborn years, the unborn incarnations, eager to place the seal of Triumphant Karma - Opportunity Realized - upon many an undiscovered emprise of celestial import. KARMA - heaven’s answer to the Soul’s challenge!