Stored impressions determine conditions of incarnation: The ego-mind, seated in the mental body, takes lower bodies according to the impressions stored in it. These impressions determine whether individuals will die young or old; whether they will experience health or illness or both; whether they will be beautiful or ugly; whether they will suffer from physical handicaps, like blindness, or will enjoy general efficiency of the body; whether they will have a sharp or a dull intellect; whether they will be pure or impure of heart, fickle or steadfast in will; and whether they will be immersed in the pursuit of material gains or will seek the inner light of the spirit.
Game of duality: The ego-mind, in its turn, becomes modified through the deposited impressions of karma, which include not only gross and physical action but thought and feeling. And the circumstances of each incarnation are adjusted to the composition and needs of the ego-mind. Thus, if a person has developed certain special capacities or tendencies in one incarnation, he takes them on to the succeeding incarnations. Similarly, things that have been left incomplete in one incarnation can be completed in the incarnations that follow. Through the persistence of impressions, the karmic links that have been forged in one incarnation are carried on and developed in succeeding incarnations. Those. who have been closely associated with each other through good or bad dealings therefore tend to have recurring contacts. Thus the game of duality is carried on long enough to gather so much experience of the opposites that the soul, out of the fullness of its experience, eventually becomes ripe for dropping the ego-mind and turning inward to know itself as the Oversoul.
-Discourses 7th Ed., p328