Chazal tell us that whoever refrains from gazing at what he shouldn’t see – and certainly at another man’s wife – will not fall under the sway of his yeitzer hora. The Ben Yehoyada (Sotah 8) notes that the gematria of ראיה , seeing, is identical to גבורה, might. We must use all our might to control what our eyes see, because this is where the yeitzer hora gets his foot in the door.
The Chafetz Chaim says the eyes are the key entry point for desire to come in and grip our soul. This is alluded to in Eicha (3:51), עיני עוללה לנפשי – it was their eyes that ruined their souls. Everything else was merely a completion of what the eyes had begun by introducing the cancerous cells.
Rashi in Vayeitzei (Bereishis 28:13) points out that Hashem associated His Name with Yitzchak Avinu during his lifetime, which was not the case with either Avraham or Yaakov. This is because Yitzchak was already blind and, consequently, his yeitzer hora was locked out.
The Chafetz Chaim warns that, although the bracha before performing a mitzvah reads, אשר קדשנו במצוותיו – Who sanctifies us through His mitzvos, i.e. that by performing mitzvos we become holy people – this transformation can only happen to those who are cautious about where their eyes and imagination travel.
Absent that vital ingredient, and one who performs a mitzvah won’t receive the ultimate promise of – אשר קדשנו being sanctified through it. Vanished is the fragrant bouquet that might have been the והייתם קדושים לאלוקיכם, being holy to Hashem. Eyes that snoop in unclean places taint the mitzvah and destroy its vitamins. By casting interested gazes where forbidden, one’s soul becomes stained and, with time, the strength of his yeitzer tov is sapped.
Imagine a house piled high with dirt and rubbish, and someone comes along to decorate it with lovely, artistic ornaments. ״What a pity!״ you say. First he must clean the place up, and only then is it fit for the crystal chandeliers, the graceful furniture and the elegant tableware. A mitzvah, like a polished diamond, calls for a pure setting.
If you long for the elated feeling of constantly connecting to Hashem, then you can work on fulfilling the six constant mitzvos – the sixth of which is not to stray after your heart and eyes. You are then on the way to reaching the level of שויתי ד' לנגדי תמיד – I have set Hashem before me always (Tehillim 16:8) – the constant awareness of Hashem’s Presence in front of you.
The hallmark of the eved Hashem is, and always has been, a constant inner striving to exercise control over his natural tendencies. Relentlessly, he seeks to subdue not others, but himself – and thereby re-make all the parts of his character into something nobler, an ever increasingly refined person. In his program of dedicating himself to Hashem he will accord shmiras einayim urgent priority.