The Torah says "שֹׁפְטִים וְשֹׁטְרִים תִּתֶּן-לְךׂ בְּכָל-שְׁעָרֶיךׂ," Judges and officials you are to provide for yourselves within all your gates (דברים טז יח). This is a general commandment to Klal Yisroel to establish a judiciary system and appoint judges upon entering the Eretz Yisroel. The Shelah Hakadosh, through defining this possuk as an individual instruction to each person, famously explains that it also indicates the importance of guarding our senses. Here, we are told to appoint "judges" at the "gates" through which all content enters and exits the body, such as the eyes, ears, nose, and mouth.
This means that we are obligated to carefully monitor and judge everything that enters and exits our body to ensure that it aligns with רְצוֹן הַשֵׁׁם. By doing so, we protect ourselves from negative influences and maintain a strong connection to השי"ת. Practicing self-judgment and self-control is a crucial part of עֲבוֹדַת הַשֵׁׁם and is essential for leading a holy, Yiddishe life.
(של"ה שופטים דרך חיים אות לב)
Yet, although all of our senses must be controlled intensely and guarded at all times, when striving for sanctity, the first sense one should concentrate on is his eyesight. According to the Tiferes Shlomo, the key to a persons kedusha lies in his efforts to guard his eyes. He says that this is hinted at in the possuk "אַיֵּה הַקְּדֵשָׁה הִוּא בַעֵּיֽנַיִם עַל-הַדָּֽרֶךְ," which can be interpreted to say "Where is the holiness? It lies in the eyes on the street," implying that kedusha can only be attained by appropriately guarding one's eyes while on the street.
(תפארת שלמה בלק ד"ה וכסה)
The same is said regarding teshuvah. When a person wants to repent and leave all his bad habits behind, he should start with placing the יצר טוב in command of his eyes. Tzadikim reference the possuk "בְּשׁוּבִי אֶת-שְׁבוּתֵיכֶם לְעֵיֽנֵיכֶם אָמַר ה'" in this context, saying that בְּשׁוּבִי can be understood to mean תְּשׁוּבָה, which starts by focusing on לְעֵיֽנֵיכֶם, the eyes. When one wishes to return to Hashem through teshuva, he should first and foremost focus on safeguarding his eyesight.