Radak: They delve deeply in their thoughts to hide their counsel from Him. They think that He does not supervise matters of the land. Therefore, they do all their desires. They say that no one sees or knows.

Malbim: Above, it discussed people who said that man cannot understand Hashem's words. Now it addresses others, who say that Hashem does not understand man's affairs. They denied Nevu'ah; Hashem would not supervise people's matters and give to them Nevu'ah. They said that sight is only via physical eyes; Hashem lacks them, so He cannot see what depends on time and place. They investigated deeply, and said that if knowledge increases, the knower must increase. Hashem cannot change! This was one of the four claims of the Greek philosophers. Also refer to 29:15:2:2, 29:15:3:2, 29:15:4:1.

Rashi: It is like "Lehastir Etzah" (to hide counsel).

Malbim: They said that if Hashem knows man's counsel (thoughts) and choices, this would change Him (His knowledge), and this cannot be.

Radak: It is as if their deeds are in a dark place where people do not see them - so they think that all their deeds, covert and open, Hashem does not see them. Yonason translates like this.

Malbim: They said that knowledge must become part of the one who knows it. Light and darkness cannot be joined. Dark physicality cannot be embodied in Hashem.

Malbim: They said that sight precedes knowledge. After seeing, intellect dissects the matter to understand the concepts. Hashem does not see with physical eyes, so how can He know?!