Derekh Hashem, Part Four, On Torah Study

And the second condition is refinement of [one's] actions. For it is fitting for one who wants to bring down influence to be worthy and readied for the bringing down. Hence if he sullies himself with guiltiness and sins, distances himself from his Creator and is unfaithful to Him [by going] after other powers and evil - it will certainly be said about him (Psalms 50:16), "And to the wicked, God said, 'Who are you to recite My laws, etc.'" And likewise did they, may their memory be blessed, say, "Anyone who teaches Torah to an unworthy student is like one who throws a stone to Markulis (an idol)." And it is certain that the Torah of such a man will not bring down the influence that we mentioned on any level at all. And nevertheless, the Sages, may their memory be blessed, revealed a great mystery to us: If the evildoers would not abandon Torah study, in the end they would return to the good. For even if they do not have it in their power to bring down anything from in front of Him, may He be blessed - as we have written - [nevertheless,] the words of the Torah are already sanctified on their own. So they stand on their own, such that from continual occupation with them - one time after another - there will eventually be some arousal and the semblance of the tiniest emanation to the one who is occupied with them. And this is what they, may their memory be blessed, said (Eichah Rabbah, Petichta 2), "If only they had left Me and kept My Torah; for the light in it brings them back to the good." However it is obvious that these words do not apply to one who is occupied with it in a manner of frivolity and joking or to reveal understandings against the law (halakha). Rather he must at least be occupied with it like one who is occupied with other wisdoms.