Adam Clarke on Numbers 23:19

God is not a man, that he should lie - This seems to be spoken to correct the foregoing supposition of Balak that God could change his mind. Even the heathen would not allow that their supreme god could be caught in a falsity. Hence Aeschylus, in Prometh. vinct. 1068: - Ψευδηγορειν γαρ ουκ επισταται στομα Το Διον, αλλα παν επος τελει. "The mouth of Jove knows not to frame a lie;

But every word finds full accomplishment."