John Calvin on Acts 12:9

9. He knew not that it was true. He did not think that it was a vain or false visor, as Satan doth oftentimes delude men with jugglings; but true is taken in this place for that which is done naturally and after the manner of men. For we must note the contrariety [antithesis] that is between the thing itself and the vision. Furthermore, though he think that it is a vision, yet doth he willingly obey; whereby his obedience is proved, whilst that being content with the commandment of the angel alone, he doth not inquire nor reason what he must de, but doth that which he is commanded to do.