Mazel and FreeWill

 Derashos HaRan (08) For it would seem that a man, according to his mazal rebels through transgressions or pursues mitzvoth, it being stated there: "One who is born under Jupiter  will be righteous. R. Nachman b. Yitzchak said: 'He will be especially exemplary in the mitzvah of charity.' One who is born under Mars will be a spiller of blood." Now this is certainly to be wondered at. For if mitzvoth or transgressions proceed from mazal, there is no room for reward or punishment. There are two answers here. Mazal, in respect to mitzvoth and transgressions, merely predisposes; it does not compel. One who is born under Tzedek is not compelled to be a tzaddik but is only predisposed in that direction. Similarly, one who is born under Mars is not compelled to be a spiller of blood, but is predisposed to it. The reason for this is that mazal acts upon bodies until it leaves an impression in them. In spite of this, however, it does not act upon the soul, which is above it. It follows from this that everything relating to nature will be affected by mazal, but acts of mitzvah or transgression, which are above the realm of nature, will be dictated by the activity of the soul. And this is in two respects. The first: the soul, having dominion over the body, can change the evil disposition invested in it by the mazal. So that, for example, if one is born under Mars, though it is dictated by his mazal that his blood be hot and boiling, predisposed to murder, still, the soul, in its power of dominion over the body, can quiet that boiling. This is the first respect. The second: though the boiling not be quieted, the soul can turn it to good and not employ it for evil. For mazal does not dictate specific acts but only characteristics, and it is within the province of the soul to employ a single characteristic for good or for evil. This is the intent of "R. Ashi said: 'Either a thief or a blood-letter; either a slaughterer or a mohel.'" Now a slaughterer and a mohel are both possessed of the same characteristic, one manifestation of that characteristic being commendable, the other, reprehensible. It is seen, then, that a mazal cannot compel the doing of mitzvoth or transgressions but can only create a predisposition — and the soul has power over that predisposition, as we have indicated.