2 Let us see, then, what answer the Lord made to this. “Where,” say they, “is your Father?” For we have heard you say, “I am not alone, but I and the Father that sent me:” we see you alone, we do not see your Father with you; how do you say that you are not alone, but that you are with your Father? Else show us that your Father is with you. And the Lord answered them: Do ye know me, that I should show you the Father? This is indeed what follows; this is what He answered in His own words, the exposition of which we have already premised. For see what He said, “You neither know me nor my Father: if you knew me, you would perhaps know my Father also.” You say then, “Where is your Father?” As if already ye knew me; as if what you see were all that I am. Therefore because ye know not me, I do not show you my Father. You suppose me, in fact, to be a man; hence ye seek a man for my father, because “ye judge after the flesh.” But because, according to what you see, I am one thing, and another thing according to what you see not, and that I as hidden from you speak of my Father as hidden, it is requisite that you should first know me, and then ye know my Father also.
3. “For if you knew me, you would perhaps know my Father also.” He who knows all things is not in doubt when He says perhaps, but rebuking. Now see how this very word perhaps, which seems to be a word of doubting, may be spoken chidingly. Yea, a word expressive of doubt it is when used by man, for man doubts because he knows not; but when a word of doubting is spoken by God, from whom surely nothing is hid, it is unbelief that is reproved by that doubting, not the Godhead merely expressing an opinion. For men sometimes chidingly express doubt concerning things which they hold certain; that is, use a word of doubting, while in their heart they doubt not: just as you would say to your slave, if you were angry with him, “Thou despisest me; but consider, perhaps I am your master.” Hence also the apostle, speaking to some who despised him, says: “And I think that I also have the Spirit of God.” When he says, “I think,” he seems to doubt; but he is rebuking, not doubting. And in another place the Lord Jesus Christ Himself, rebuking the future unbelief of mankind, says: “When the Son of man comes, will He, do you think, find faith on the earth?”
Source: Tractates on the Gospel of John (New Advent)