We see in the Book of the Judges that the same thing happened to the captain Gedeon, to whom God had said many times that he should conquer the Madianites, yet he was fearful and full of doubts (for God had allowed him to retain that weakness) until he heard from the mouth of men what God had said to him. And it came to pass that, when God saw he was weak, He said to him: 'Rise up and go down to the camp.' Et cum audieris quid loquantur, tunc confortabuntur manus tuae, et securior ad hostium castra descendes. That is: When thou shalt hear what men are saying there, then shalt thou receive strength in that which I have said to thee, and thou shalt go down with greater security to the hosts of the enemy.
And so it came to pass that, having heard a dream related by one of the Madianites to another, wherein the Madianite had dreamed that Gedeon should conquer them, he was greatly strengthened, and began to prepare for the battle with great joy. From this it can be seen that God desired not that he should feel secure, since He gave him not the assurance by supernatural means alone, but caused him first to be strengthened by natural means.
Herein it is clearly shown that a man must not rely upon the things that God reveals, save in the way that we are describing; for, even in cases where a person is in possession of certainty, as Saint Paul was certain of his Gospel (since he had already begun to preach it), yet, although the revelation be of God, man may still err with respect to it, or in things relating to it.
For, although God reveals one thing, He reveals not always the other; and oftentimes He reveals something without revealing the way in which it is to be done. For ordinarily He neither performs nor reveals anything that can be accomplished by human counsel and effort, although He may commune with the soul for a long time, very lovingly.