John Calvin on Genesis 40:5

5. And they dreamed a dream. What I have before alluded to respecting dreams must be recalled to memory; namely, that many frivolous things are presented to us, which pass away and are forgotten; Calvin’s words are: “Quae Transeunt per portam corneam.” — Vide Virgil. Aeneid. VI. In finem. This is an obviously mistaken allusion, arising probably from a lapse of memory in Calvin, or in the transcriber of his works. He should have said “portam eburnam.” The ancient mythologists distinguished true dreams from false, by representing the former as passing through the “horny gate,” (porta cornea,) the latter through the “ivory gate,” (porta eburna.) — Ed. some, however, have the force and significance of prophecy. Of this kind were these two dreams, by which God made known the hidden result of a future matter. For unless the mark of a celestial oracle had been engraven upon then, the butler and the baker would not have been in such consternation of mind. I acknowledge, indeed, that men are sometimes vehemently agitated by vain and rashly conceived dreams; yet their terror and anxiety gradually subsides; but God had fixed an arrow in the minds of the butler and the baker, which would not suffer them to rest; and by this means, each was rendered more attentive to the interpretation of his dream. Moses, therefore, expressly declares that it was a presage of something certain.