John 16:30

It was from this diet that they drew the knowledge that He knew all things, and needed not that any one should ask Him: and, indeed, why they said this, is a topic worthy of inquiry. For one would think they ought rather to have said, Thou needest not to ask any one; not, "That any one should ask Thee." They had just said, We are sure that Thou knowest all things:" and surely He that knoweth all things is accustomed rather to be questioned by those who do not know, that in reply to their questions they may hear what they wish from Him who knoweth all things; and not to be Himself the questioner, as if wishing to know something, when He knoweth all things. What, then, are we to understand by this, that, when apparently they ought to have said to Him, whom they knew to be omniscient, Thou needest not to ask any man, they considered it more befitting to say, "Thou needest not that any man should ask Thee"? Yea, is it not the case that we read of both being done; to wit, that the Lord both asked, and was asked questions? But this latter is speedily answered: for this was needful not for Him, but for those rather whom He questioned, or by whom He was questioned. For He never questioned any for the purpose of learning anything from them, but for the purpose rather of teaching them. And for those who put questions to Him, as desirous of learning something of Him, it was assuredly needful to be made acquainted with some things by Him who knew everything.

(Tr. ciii. 2) Why this remark? To one Who knew all things, instead of saying, Thou needest not that any man should ask Thee; it would have been more appropriate to have said, Thou needest not to ask any man: yet we know that both of these were done, viz. that our Lord both asked questions, and was asked. But this is soon explained; for both were for the benefit, not of Himself, but of those whom He asked questions of, or by whom He was asked. He asked questions of men not in order to learn Himself, but to teach them: and in the case of those who asked questions of Him, such questions were necessary to them in order to gain the knowledge they wanted; but they were not necessary to Him to tell Him what that was, because He knew the wish of the enquirer, before the question was put. Thus to know men's thoughts beforehand was no great thing for the Lord, but to the minds of babes it was a great thing: By this we know that Thou camest, forth from God.

The inward state of Christ's disciples, when before His passion He talked with them as with children of great things, but in such a way as befitted the great things to be spoken to children, because, having not yet received the Holy Spirit, as they did after His resurrection, either by His own breathing upon them, or by descent from above, they had a mental capacity for the human rather than the divine, is everywhere declared through the Gospel by numerous testimonies; and of a piece therewith, is what they said in the lesson before us. For, says the evangelist, "His disciples say unto Him: Lo, now speakest Thou plainly, and utterest no proverb. Now we are sure that Thou knowest all things, and needest not that any man should ask Thee: by this we believe that Thou camest forth from God." The Lord Himself had said shortly before, "These things have I spoken unto you in proverbs: the hour cometh, when I shall no more speak to you in proverbs." How, then, say they, "Lo, now speakest Thou plainly, and utterest no proverb"? Was the hour, indeed, already come, when He had promised that He would no more speak unto them in proverbs? Certainly that such an hour had not yet come, and when thus that hour is still the subject of promise when He was to speak without proverbs, why say they, "Lo, now speakest Thou plainly, and utterest no proverb;" but just because those things, which He knows to be proverbs to those who have no understanding, they are still so far from understanding, that they do not even understand that they do not understand them? For they were babes, and had as yet no spiritual discernment of what they heard regarding things that had to do not with the body, but with the spirit.

By this the holy Apostles did not understand that He had gone forth, in the sense of having been sent, from God. For they had often heard Him confess, in His earlier discourses, that He was sent; but what they hear now is the express statement that He had gone forth from God. This opens their eyes to perceive from His works His Divine nature. The fact that He had gone forth from God makes clear to them His true Divinity, and so they say, "Now therefore we are sure that Thou knowest all things, and needest not that any man should ask Thee; by this we believe that Thou wentest forth from God." The reason why they believe that He went forth from God is that He both can, and does, perform the works of God. Their perfect assurance of His Divine nature is the result of their knowledge, not that He is come from God, but that He did go forth from God. Accordingly we find that it is this truth, now heard for the first time, which clenches their faith. The Lord had made two statements; "I went forth from God," and "I am come from the Father into this world." One of these, "I am come from the Father into this world," they had often heard, and it awakens no surprise. But their reply makes it manifest that they now believe and understand the other, that is, "I went forth from God." Their answer, "By this we believe that Thou wentest forth from God," is a response to it, and to it only; they do not add, "And art come from the Father into this world." The one statement is welcomed with a declaration of faith; the other is passed over in silence. The confession was wrung from them by the sudden presentation of a new truth, which convinced their reason and constrained them to avow their certainty. They knew already that He, like God, could do all things; but His birth, which accounted for that omnipotence, had not been revealed. […]

(Hom. lxxix. 2) But since His answer met what was in their minds, they add, Now we are sure that Thou knowest all things. See how imperfect they yet were, after so many and great things now at last to say, Now we are sure &c. saying it too as if they were conferring a favour. And needest not that any man should ask thee; i. e. Thou knowest what offends us, before we tell Thee, and Thou hast relieved us by saying that the Father loveth us.