Then shall his mind change, and he shall pass over, and offend, imputing this his power unto his god.
Then - when elated by his successes.
Shall his mind change - he shall lose whatever of reason or moderation ever was in him, with pride.
And he shall pass over - all bounds and restraints: his pride preparing the sure way for his destruction (Proverbs 16:18). The language is very similar to that describing Nebuchadnezzar's "change" from "man's heart" (understanding) to that of a "beast," because of pride (Daniel 4:16; Daniel 4:30-34; see notes there). An undesigned coincidence between the two sacred books, written independently.
And offend, imputing this his power unto his god - (Daniel 5:4). Sacrilegious arrogance, in ascribing to his idol, Bel, the glory that belongs to God (Calvin). Grotius explains, '(saying that) his power is his own, as one who is a god to himself,' (cf. Habakkuk 1:16; and Daniel 3:1-30.) So Maurer, 'He shall offend as one to whom his power is his god' (note, Job 12:6, 'who make a god of their own hand;' Micah 2:1, "They practice it (iniquity), because it is in the power of their hand").