NUM196 Do not stray after your heart and eyes. Our Sages explain (Berachos 12b), “After your hearts” refers to heresy (מינות-minus). That is, do not ponder ideas that contradict the Torah way of thinking, because occupying one’s thoughts with such ideas can lead one to heresy--to completely deny the Torah’s most fundamental teachings. If such non-Torah ideas enter one's mind, one immediately must cut short such musings. One must turn one’s thought to Torah matters--to the true and the good. “After your eyes,” say our Sages, refers to immortality. That is, do not chase after what the eye sees. Included is not to chase after any of the alluring physical pleasures of this world, for succumbing to mundane lust leads only to shame and woe. Both “after your hearts” and “after your eyes” apply equally to men and women. Key concepts: This mitzvah is central to Judaism, because by heeding it one is saved from sinning against Hashem all of one's life. Unworthy thoughts are fathers of impurity, for their offspring are sinful deeds. He who keeps his mind free of improper thoughts will not sin and thereby will merit all blessings. Realize, and repeat verbally, “One sin leads to another (עבירה גוררת עבירה),” and “One mitzvah leads to another (מצוה גוררת מצוה).” If you allow yourself to gratify a physical lust once, it will drag you into gratifying it again and again. On the other hand, if you are strong and resist the enticement, turning your eyes away from the evil, then even if you do so only once, you will find it easier to do so again and again. That is, just as wine entices a drunkard, physical attractions entice the body and bring about its ruin. If one becomes accustomed to always gratifying one’s physical desires, one’s evil inclination grows stronger every day, and one becomes enslaved to it. By contrast, if a person stubbornly resists temptation and abstains from gratifying his physical desires--choosing to take control--he rejoices in his portion all the day. Accordingly, this is one of the “constant” mitzvos. One is obligated never to follow after one's heart or eyes all of the days of one's life. I mentioned this point in the Introduction to Sefer HaChinuch [cited in the Mishnah Berurah, Siman 1 in the Biur Halachah, s.v. Hu klal]. He who violates this mitzvah--letting his thoughts dwell on the matters that cause one to stray from the perfect and pure ways of the Torah--will find himself in bitterness and evil. He will have sullied himself by entering the foolish mindset of heretics. So, too, he who strays after his eyes--chasing after this world’s physical pleasures, seeking repeated gratification of all sorts of mundane desires with no intent to use such pleasures for the good--instead of using these pleasures to promote his health so that he can actually serve his Maker. Striving only to gratify his baser nature, he constantly violates this basic and constant mitzvah.