When Hashem breathed life into Adam Harishon, He breathed from Himself, so to speak. Something of divinity entered the founder of our race right from his very first breath of life. The soul of man is a spark of the divine; its spiritual source is higher than that of the heavenly angels.
Think of the vast expanses of outer space. Then think how the soul Hashem placed within you is similarly vast, though in a different dimension. Your neshama was hewn from Hashem's own throne. Let us not underestimate who we are.
We have a principle that Hashem, in His kindness, has appointed Am Yisrael as Heaven's policy makers - He takes their cues and acts accordingly. ״Little״ me is a lynchpin in myriads of spiritual worlds.
When we do mitzvos, we are in fact pressing all the right buttons on the control panel of the universe. Even a single rejection of the impure will uphold countless spiritual worlds. But please note that it also works the other way around, and even one instance of giving in to temptation destroys accordingly.
It is not surprising then, that some Amora'im chose to be blind so as to never see impure sights. However, they were an exception. From the rest of us, Hashem wants the rest of us to keep the amazing gift of eyesight, and use it to carry out His mitzvos.
Kabbalistic sources tell us of the cosmic effects of restricting one's eyes from grazing in foreign pastures. The three colours of the eye correspond to the three avos. This lofty concept and many more similar ones regarding the eyes are discussed in Reishis Chochmah (see Sha'ar Hakadusha, ch. 8) and other sefarim, and though their true meaning may be beyond our grasp, they at least give an inkling of the colossal effects of our shmiras einayim.
Shmiras einayim is literally a life-giving elixir, free to all. The Ibn Ezra finds a hint to this in Tehillim (119:37), where Dovid Hamelech begs Hashem, העבר עיני מראות שוא בדרכיך חייני - Avert my eyes from seeing futility, preserve my life through Your ways.
All the inconvenience of looking down, looking away, staying away, curtailing travel and leisure options, and so much more, will be paid for in handsome dividends to us, to our children and to our children's children, writes the Sefer Chassidim (siman 495).
If the Torah promises generous reward for not tasting animals' blood, something we would in any case find disgusting, then how much greater is the reward for controlling our base drives for viewing things that beckon and captivate.
King Achaz was a sinner, yet he took care never to rest his eyes on women. For this saving grace, the Navi Yeshaya promised him sure victory in all his wars.