John Calvin Commentary John 16:4

"But these things have I spoken unto you, that when their hour is come, ye may remember them, how that I told you. And these things I said not unto you from the beginning, because I was with you." — John 16:4 (ASV)

That when the hour cometh, you may remember. He repeats what he had already said: that this is not a philosophy suited only for a season of leisure, but one adapted to practice and use. He now speaks on these matters so that they may actually demonstrate that they have not been taught in vain. When he says, that you may remember, he instructs them, first, to store in their minds what they have heard; secondly, to remember them when they are required to put them in practice; and, lastly, he declares that no small importance is attached to the fact that he makes predictions of future events.

And I told you not these things at the beginning. As the apostles were still weak and tender, their singularly good and indulgent Master spared them as long as Christ was with them in the flesh. He did not allow them to be urged beyond what they were able to bear. At that time, therefore, they had no great need of confirmation while they enjoyed leisure and freedom from persecution. But now he tells them that they must change their mode of life, and as a new condition awaits them, he likewise exhorts them to prepare for a conflict.