Rashi on Deuteronomy 4:19/רש"י על דברים ד׳:י״ט

1ופן תשא עיניך AND LEST THOU LIFT UP THINE EYES to ponder on the matter, and to set your heart to go astray after them.

2אשר חלק ה׳ WHICH THE LORD ASSIGNED to give light to them (to all peoples) (Megillah 9b). — Another explanation: which God assigned to them as deities; He did not prevent them from going astray after them, but He allowed them to err (to slip) through vain speculations, in order to drive them out from the world. Similarly it states, (Psalms 36:3) "He (God) made him err (slip) through his eyes (i.e. through what his eyes behold) until his iniquity be found and he be hated” (Avodah Zarah 55a).