Here are a few words on the effect of karma on the mind, from the Bhagawad Gita.
Material Constituent of Thought, Mind & Karma
Your mind which is the generating force of thought has involuntarily divided itself into flexible compartments. Thus a section of your waking mind associates itself with the physical and is so closely identified with it that it dies with the physical body. It
recognizes no other thought except the purely material idea of the world. If I ask that mind to imagine a. non-material world it refuses to function, that is, by saying that I can reach the stars it will look suspicious aiid ask me how long I would take to reach my destination and whether I would not be killed by the heat or what I could get there for food. In other words, it will only conceive of the physical and the material thoughts which pertain to the life of the physical body.
Etheric Constituent of Thought
Next in order, but exactly similar, is that section of the mind which identifies itself with your emotional existence. This recognises no other truth than the thoughts created by the feelings which arise in the etheric body in the fifth plane. The idea of the fifth dimension is perceptible to those who have crossed the fifth plane, for till then the fact that thought creates action is not realized in practical life.
Residual Impact of Karma on Inner Mind
Thus, when the soul reincarnates nothing of what happened in the prior life is remembered since both sections of the mind which can relate your past life are now dead. What remains is the exact mathematical and algebraic sum-total of the impacts which the Inner Mind has had during its sojourn in association with the etheric and physical sections of your mental mechanism.
Do not wonder why I tell you all this before telling you what is the fifth, sixth or the seventh dimension. I have been at pains to speak about the physical event as having^ been caused by the non-physical entity called ‘thought Thought which emanates from the mind produces action and what results in the mind is the reflex action of that thought against the Self himself.
What is Karma?
First of all, what is karma? This reflex which you call Karma gets more and more pronounced so long as the thought has emanated and is emanating from the etheric and physical sections of the individual’s mind.
This potential factor which is the measure of the soul’s immersion in pleasure or pain possesses the chief dynamic element of your Self and having obtained the reins of the Self’s fate, begins to drive and steer the refractory steed relentlessly and with unmerciful and terrible accuracy against the Self himself. This relentless drive is the mere causation of the thought of the Inner Mind in the grips of Karma.
Your fate is the effect of the thought of your Inner Mind in the control of Karma. If I am beaten by a ruffian I must have liberated that identical thought by my Karma which, for the time, has had the control of my Inner Mind. Without this thought, which’ has acted against the Self, no event could happen prejudicial to the Self.