John 14:29

(Tract. lxxix. 1) But is not the time for belief before a thing takes place? Is it not the praise of faith, that it believes what it does not see? according to what is said below to Thomas: Because thou hast seen, thou hast believed. He saw one thing, believed another: what he saw was man, what he believed was God. And if belief can be talked of with reference to things seen, as when we say that we believe our eyes; yet it is not mature faith, but is merely preparatory to our believing what we do not see. When it has come to pass; then He says, because after His death they would see Him alive again, and ascending to His Father; which sight would convince them that He was the Christ, the Son of God; able as He was to do so great a thing, and to foretell it. Which faith however would not be a new, but only an enlarged faith; or a faith which had failed at His death, and been renewed by His resurrection.

Our Lord and Saviour, Jesus Christ, had said unto His disciples, "If ye loved me, ye would surely rejoice, because I go unto the Father; for the Father is greater than I." And that He so spake in His servant-form, and not in that of God, wherein He is equal with the Father, is well known to faith as it resides in the minds of the pious, not as it is reigned by the scornful and senseless. And then He added, "And now I have told you before it come to pass, that, when it is come to pass, ye might believe." What can He mean by this, when the fact rather is, that a man ought, before it comes to pass, to believe that which demands his belief? For it forms the very encomium of faith when that which is believed is not seen. For what greatness is there in believing what is seen, as in those words of the same Lord, when, in reproving a disciple, He said, "Because thou hast seen, thou hast believed; blessed are they that see not, and yet believe." And I hardly know whether any one can be said to believe what he sees; for this same faith is thus defined in the epistle addressed to the Hebrews: "Now faith is the substance of those that hope, the assurance of things not seen." Accordingly, if faith is in things that are believed, and that, too, in things which are not seen, what mean these words of the Lord, "And now I have told you before it come to pass, that, when it is come to pass, ye might believe"? Ought He not rather to have said, And now I have told you before it come to pass, that ye may believe what, when it is come to pass, ye shall see? For even he who was told, "Because thou hast seen, thou hast believed," did not believe only what he saw; but he saw one thing, and believed another: for he saw Him as man, and believed Him to be God. He perceived and touched the living flesh, which he had seen in the act of dying, and he believed in the Deity infolded in that flesh. […]

(Hom. lxxv. 4) Or thus: The Apostles did not yet know what the resurrection was of which He spoke when He said, I go, and come again to you; or what they ought to think of it. They only knew the great power of the Father. So He tells them: Though ye fear I shall not be able to save Myself, and do not trust to My appearing again after My crucifixion; yet when ye hear that I go to My Father, ye should rejoice, because I go to one greater, one able to dissolve and change all things. All this is said in accommodation to their weakness: as we see from the next words; And now I have told you before it come to pass; that when it does come to pass, ye may believe.

And now I have told you. After the consolation has been set forth, there is here added the hastening of departure. And first is noted the reason for foretelling; second, the reason for hastening; third, the sign of the hastening. There is noted, therefore, first …

He now answers an unspoken question when he says, And now I have told you before it takes place, so that when it does take place, you may believe. For they could have asked why he was telling them these things, and so he anticipates …