John Calvin on John 14:29

29. And I have told you now. It was proper that the disciples should be frequently admonished on this point; for it was a secret far exceeding all human capacity. He testifies that he foretells what shall happen, that, when it has happened, they may believe; for it was a useful confirmation of their faith when they brought to recollection the predictions of Christ, and saw accomplished before their eyes what they had formerly heard from his mouth. Yet it appears to be a sort of concession, as if Christ had said, “Because you are not yet capable of comprehending so deep a mystery, I bear with you till the event has happened, which will serve as an interpreter to explain this doctrine.” Although for a time he seemed to speak to the deaf, yet it afterwards appeared that his words were not scattered in vain, or, as we may say, in the air, but that it was a seed thrown into the earth. Now, as Christ speaks here about his word and the accomplishment of events, so his death, and resurrection, and ascension to heaven, are combined with doctrine, that they may produce faith in us.