Albert Barnes Commentary Job 31:28

"This also were an iniquity to be punished by the judges; For I should have denied the God that is above." — Job 31:28 (ASV)

This also were an iniquity to be punished by the judge (Job 31:28) — Note Job 31:11. Among the Hebrews, idolatry was an offense punishable by death by stoning (Deuteronomy 17:2–7). It is also possible that this might have been a crime punishable in this manner elsewhere in patriarchal times. In any case, Job regarded it as a heinous offense, and one that the magistrate should take notice of.

For I should have denied the God that is above (Job 31:28) — The worship of the heavenly bodies would have been, in fact, the denial of the existence of any Superior Being. This, in fact, always occurs, for idolaters have no knowledge of the true God.