"You shall not go astray after your hearts and after your eyes" (Numbers 15:39) "After your hearts"- this refers to atheism, "After your eyes: this refers to sexual immorality (Berachot 12b). There are desires that are very difficult to control unless one has been taught from childhood, like for example, refraining from looking at women. Therefore, must a man teach and educate his sons on the right path so when they grow old they will not abandon it (Sefer Chassidim 10)
The main enjoyment in the World to Come is through the eyes of the soul (Tzadikkim sit with their crowns on their heads and contemplate the brilliance of the Shechina). But whoever damages his eyes in this world damages thereby the eyes of his soul (Od Yoseph Chai, Vaetchanan)