הלכה על שבת 134:21

From the roots of the commandment are that it is known that magic is a very bad thing and causes many mishaps to people. I do not have to write at length about it, as the things are well-known. And therefore we were commanded to put away from the world someone who makes efforts with this, as he is coming against the will of God, as He desires [the world's] settlement and that everything should be administered in a natural way. As nature was at the beginning of creation and this one wants to change everything. And according to my opinion, the matter of magic is that at the beginning of creation, God, blessed be He, placed for each and every thing in the world a nature [through which] to accomplish its action well and straight, for the good of the creatures of the world that He created; and He commanded each one to act according to its species, as it is written about all the creatures, in Parshat Bereshit (Genesis 1:12), “according to its species.” And He also made a higher force govern each and every one from above, to compel it to perform its action; as they, may their memory be blessed, said (Bereshit Rabbah 1), “There is no [blade of] grass below that does not have a constellation above that tells it, 'Grow!'”And besides the action that each and every one does according to its nature, there is another action that they have, by mixing one specie with another. And in the craft of this mixing there are some angles that were not permitted for people to utilize, because God knows that the end result that will come out for people from these angles will be bad for them. And on account of this, He prevented them from them. And this is what they, may their memory be blessed, said more generally (Shabbat 67b), “Anything that has healing in it does not have the 'ways of the Amorite' in it”; meaning to say, it should not be forbidden from the perspective of magic – since there is a benefit to it that is found from true experience, it is not from the forbidden angles, as they are only forbidden because of the perspective of their damage. And there is another matter in these forbidden angles of mixture and machinations for which they were forbidden. [It is] because the power of this mixture is so strong that it negates the power of the constellations that are assigned upon the two species. And the illustration of this is that it is just like that which you see with the grafting of one specie with a different one, that a new third specie is created. It comes out that the grafting negates the power of both of them. And so we have been prevented from bringing up to our minds to switch the perfect acts of God, even if something that appears to be pleasing comes out in our hand.