John Calvin Commentary Numbers 24:15

"And he took up his parable, and said, Balaam the son of Beor saith, And the man whose eye was closed saith;" — Numbers 24:15 (ASV)

Balaam the son of Beor has said. Since he was preparing to address most important matters, it is not without reason that he renews his preface to obtain more authority for his prophecy; and although it was not without ambition that he proclaimed these magnificent titles, still we cannot doubt that God would ratify by them what He had determined to deliver through the prophet. It was necessary that this worthless man, whose doctrine would otherwise have been contemptible, should be marked out by divine indications; and so he assumed a character that he did not possess and attributed to himself what belongs only to true prophets.

I have previously explained how the open and the closed eye are spoken of in the same sense, though for different reasons: for he calls the eye “hidden,” as perceiving the secret things of darkness, which are incomprehensible to human understanding; but he claims for himself “open eyes,” because he beholds by prophetic vision what he is about to say, as if he would deny that he was going to speak of things that were obscure and scarcely intelligible to himself.