If we go more deeply into this, the fact becomes apparent that the external career of a man in one incarnation, when it is not merely a career but also an inner vocation, passes over in his next incarnation into the inward shaping of his bodily organs. Thus, if a man has been an exceptionally good mathematician in one incarnation, the mastery he has obtained over numbers and figures remains with him and goes into a special development of his sense-organs, for instance, of the eyes. People with very good sight have it as a result of the fact that in their former incarnation they thought in forms; they took this thinking in forms with them and during the life between death and rebirth they worked specially on the shaping of their eyes. Here the mathematical talent has passed into the eyes and no longer exists as a gift for mathematics.
Another case known to occultists is where an individuality in one incarnation lived with intensity in architectural forms; these experiences lived as forces in his inner soul-life and worked strongly upon the instrument of hearing, so that in his next incarnation he became a great musician. He did not appear as a great architect, because the perception of form necessary for architecture was transformed into an organ-building force, so that there was nothing left but a supreme sensitiveness for music.
An external consideration of similarities is generally deceptive in reference to the characteristics of successive incarnations; and just as we must reflect upon whatever did not please us and conceive of ourselves as having had an intense desire for it, so we must also reflect upon those things for which we have the least talent, and about which we are stupid. If we discover the dullest sides of our nature, they may very probably point to those fields in which we were most brilliant in our previous incarnation. Thus we see how easy it is in these matters to begin at the wrong end. A little reflection will show us that it is the soul-kernel of our being which works over from one incarnation to another; this can be illustrated by the fact that it is no easier for a man to learn a language even if in his preceding incarnation he lived in the country associated with this particular language; otherwise our school-boys would not find it so difficult to learn Greek and Latin, for many of them in former incarnations will have lived in the regions where these were the languages of ordinary intercourse.
You see, the outer capacities we acquire are so closely connected with earthly circumstances that we cannot speak of them reappearing in the same form in the next incarnation; they are transformed into forces and in that way pass over to a subsequent incarnation. For instance, people who have a special faculty for learning languages in one incarnation will not have this in the next; instead, they will have the faculty which enables them to form more unbiassed judgments than those who had less talent for languages; these latter will tend to form one-sided judgments.
Source: Rudolf Steiner – GA 135 – Reincarnation and Karma – I – Berlin, 23rd January 1912