A person’s level of kedusha depends on shemiras einayim. Therefore, one must be extremely careful regarding what he looks at. Chazal say (Bava Basra 2B): “Hezek riya shmei hezek (damage caused by the eyes is considered damage).” The word “shmei” has the same letters as “shem Kah” (the name of Hashem), which indicates that one who isn’t careful with what he sees damages the name of Hashem.
With this in mind, he explains the words Balak told Bilaam: “And they cover (v’chisa) the eye of the land.” This can be understood to mean that they cover their eyes from seeing improper things, which is why Balak was afraid of them. Bilaam, however, had “open eyes”. He looked at whatever he wanted, so he remained on a low level.
כִּנְחָלִים נִטָּיוּ כְּגַנֹּת עֲלֵי נָהָר כַּאֲהָלִים נָטַע ה' וגו' (כו, ד)
They extend like streams, like gardens by the river, like aloes which Hashem planted. (26:4)
The Lowlier One Is, The More He Will Rise:
Rav Noach of Lechovitch zy”a (quoted in Toras Avos) explains the words “ganos” (gardens) to mean “to demean” (meganeh). He thus understands the pasuk to be saying that the lowlier a person holds himself, the more he will merit “alei nahar”, which symbolizes to be illuminated (l’hair) with the Divine light.
