50 And I know that his commandment is life everlasting: whatsoever I speak therefore, even as the Father said unto me, so I speak.
[AD 407] John Chrysostom on John 12:44-50
(Hom. lxviii. 1) Because the love of human praise prevented the chief rulers from believing, Jesus cried and said, He that believeth on Me, believeth not on Me, but on Him that sent Me: as if to say, Why are ye afraid to believe on Me? Your faith through Me passes to God.

(Hom. lxix. 1) He that believeth on Me, believeth not on Me, but on Him that sent Me: as if He said, He that taketh water from a stream, taketh the water not of the stream, but of the fountain. Then to show that it is not possible to believe on the Father, if we do not believe on Him, He says, He that seeth Me, seeth Him that sent Me. What then? Is God a body? By no means; seeing here is the mind's vision. What follows still further shows His union with the Father. I am come a light into the world. This is what the Father is called in many places. He calls Himself the light, because he delivers from error, and disperses the darkness of the understanding; that whosoever believeth in Me should not abide in darkness.

(Hom. lxix. 1) And to show that He does not let His despisers go unpunished, from want of power, He adds, And if any man hear My words and believe not, I judge him not.

(Hom. lxix. 2) But that this might not serve to encourage sloth, He warns men of a terrible judgment coming; He that rejecteth Me, and heareth not My words, hath one that judgeth him.

(Hom. lxviii. 2) Or, I judge him not, i. e. I am not the cause of his destruction, but he is himself, by despising my words. The words that I have just said, shall be his accusers, and deprive him of all excuse; the word that I have spoken, the same shall judge him. And what word? This, viz. thatf I have not spoken of Myself, but the Father which sent Me gave Me a commandment what I should say, and what I should speak. All these things were said on their account, that they might have no excuse.

[AD 430] Augustine of Hippo on John 12:44-50
(Tr. liii. 13) As their faith grew, their love of human praise grew still more, and outstripped it.

(Tr. liv. 2) He signifies to them that He is more than He appears to be, (for to men He appeared but a man; His Godhead was hid.) Such as the Father is, such am I in nature and in dignity; He that believeth on Me, believeth not on Me, i. e. on that which He sees, but on Him that sent Me, i. e. on the Father. [1He that believes in the Father must believe in Him as the Father, i. e. must believe that He has a Son; and reversely, he who believes in the Son thereby believes in the Father.] And again, if any one thinks that God has sons by grace, but not a Son equal and coeternal with Himself, neither does he believe 2on the Father, who sent the Son; because what he believes on is not the Father who sent Him. (c. 3.). And to show that He is not the Son, in the sense of one out of many, a son by grace, but the Only Son equal to the Father, He adds, And He that seeth Me, seeth Him that sent Me; so little difference is there between Me and Him that sent Me, that He that seeth Me, seeth Him. Our Lord sent His Apostles, yet none of them dared to say, He that believeth on Me. We believe an Apostle, but we do not believe on an Apostle. Whereas the Only Begotten says, He that believeth on Me, doth not believe on Me, but on Him that sent Me. Wherein He does not withdraw the believer's faith from Himself, but gives him a higher object than the form of a servant, for that faith.

(Tr. liv. 4) Whereby it is evident, that He found all in darkness. In which darkness if they wish not to remain, they must believe in the light which is come into the world. He says in one place to His disciples, Ye are the light of the world; but He did not say to them, Ye are come a light into the world, that whosoever believeth on you should not abide in darkness. All saints are lights, but they are so by faith, because they are enlightened by Him, from Whom to withdraw is darkness.

(Tr. liv. 5, 6) i. e. I judge him not now. He does not say, I judge him not at the last day, for that would be contrary to the sentence above, The Father hath committed all judgment unto the Son. (5:22) And the reason follows, why He does not judge now; For I came not to judge the world, but to save the world. Now is the time of mercy, afterward will be the time of judgment.

(Tr. liv. 6) Mean time they waited to know who this one was; so He proceeds: The word that I have spoken, the same shall judge him at the last day. He makes it sufficiently clear that He Himself will judge at the last day. For the word that He speaks, is Himself. He speaks Himself, announces Himself. We gather too from these words that those who have not heard, will be judged differently from those who have heard and despised.

(i. de Trin. c. xii. [26.]) I judge him not; the word that I have spoken shall judge him: for I have not spoken of Myself. The word which the Son speaks judges, because the Son did not speak of Himself: for I have nut spoken of Myself: i. e. I was not born of Myself.

AUGUSTINE.e I ask then how we shall understand this, I will not judge, but the word which I have spoken will judge? Yet He Himself is the Word of the Father which speaketh. Is it thus? I will not judge by My human power, as the Son of man, but as the word of God, because I am the Son of God.

(Tr. liv. 7) When the Father gave the Son a commandment, He did not give Him what He had not: for in the Wisdom of the Father, i. e. in the Word, are all the commandments of the Father. The commandment is said to be given, because it is not from him to whom it is said to be given. But to give the Son that which He never was without, is the same as to beget the Son who never was not.

(Tr. liv) If life everlasting is the Son Himself, and the commandment is life everlasting, what is this but saying, I am the commandment of the Father? And in the same way in the following; Whatsoever I speak therefore, even as the Father said unto Me, so I speak, we must not understand, said unto Me, as if words were spoken to the Only Word. The Father spoke to the Son, as He gave life to the Son; not that the Son knew not, or had not, but that He was the Son. What is meant by, as He said unto Me, so I speak, but that I am the Word who speaks. The Father is true, the Son is truth: the True, begat the Truth. What then could He say to the Truth, if the Truth was perfect from the beginning, and no new truth could be added to Him? That He spake to the Truth then, means that He begat the Truth.

[AD 1107] Theophylact of Ohrid on John 12:44-50
Since the Son is the Word of the Father, and reveals completely what is in the mind of the Father, He says He receives a commandment what He should say, and what He should speak: just as our word, if we say what we think, brings out what is in our minds.
And I know that His commandment is life everlasting.

[AD 220] Tertullian on John 12:50
For "the Lord God hath given me the tongue of the learned, that I should know when I ought to speak" the word which I actually speak. "Even as the Father hath said unto me, so do I speak." Now, in what way these things were said to Him, the evangelist and beloved disciple John knew better than Praxeas; and therefore he adds concerning i his own meaning: "Now before the feast of the passover, Jesus knew that the Father had given all things into His hands, and that He had come from God, and was going to God.

[AD 407] John Chrysostom on John 12:50
Do you see the humility of the words? For he who has received a commandment is not his own master. Yet he says, “As the Father raises up the dead and enlivens them, even so the Son enlivens whom he will.” Does he have power then to enliven whomever he wants, and does he not have the power to say what he wants? What he intends then by the words is this: It is not possible that he [the Father] should speak one set of words and I should utter another. “And I know that his commandment is life everlasting.” He said this to those who called him a deceiver and who asserted that he had come to do harm. However, when he says “I judge not,” he shows that he is not the cause of their destruction. By this he all but plainly testifies (when he is about to remove himself from them and leave) that “I converse with you, speaking nothing on my own but everything as from the Father.”

[AD 430] Augustine of Hippo on John 12:50
If life everlasting is the Son himself and the commandment is life everlasting, what is this but saying, “I am the commandment of the Father”? And in the same way in the following, “Whatever I speak therefore, even as the Father said to me, so I speak,” we must not understand “said to me” as if words were spoken to the only Word or that the Word of God needed words from God. The Father spoke to the Son in the same way as he gave life to the Son. It was not that the Son was ignorant or did not [already] have life. Rather, it was simply because the Son was what he was. What, then, is meant by “as he said to me, so I speak” but that I am the Word who speaks. The Father is true, the Son is truth: the True begat the Truth. What then could he say to the Truth if the Truth was perfect from the beginning and no new truth could be added to him? That he spoke to the Truth then means that he begat the Truth.

[AD 444] Cyril of Alexandria on John 12:50
And I think that this would really suffice: yet I will also say something else by way of exposing the insolence of their loquacity. For come now, if it seems good to thee, and let us, having summarized for the present occasion in few words the doctrine of the Incarnation, show concerning the Only-Begotten Himself that it was well and rightly said: I speak not from Myself; but the Father which sent Me, He hath given Me a commandment what I should say and what I should speak. For being Himself the Living and Personal Word of God the Father, He is necessarily the medium of interpreting what is in the Father; and in bringing to light that which is, as it were, the set will and purpose of His own Father, He says He has in effect received a commandment: and any one might see even in the case of ourselves that the fact is truly so and could not be otherwise. For the language of utterance, which consists in the putting together of words and phrases, and which makes itself heard externally by means of articulate speech, reveals that which is in the intellect, when our intellect gives a commandment as it were to it; although indeed the whole process does not take much time. For, the moment it has decided upon anything, the mind at once delivers it over to the voice; and the voice, passing outwards, interprets what is in the innermost depth of the mind, altering nothing of what it has been commanded to utter. "Where then is the strange part of the matter, sirs," any one might very well say to our opponents, "if the Son, being the Word of God the Father, does (in a manner not indeed exactly like ours, for the ways of God transcend all comparison,) interpret the will of Him Who begat Him?" For does not the prophet speak of Him as called by a title most fitting for Him: "Angel of great counsel?" But this I think is quite clear. The Only-Begotten therefore will suffer no detraction as regards His Essence or His dignity, even though He is said to have received a commandment from God the Father: for we ourselves also are often commanding others and ordering them to do something, but they will not on this account deny their community of nature with us, nor will they lose their likeness to us or be less consubstantial with us, whether before or after the utterance of the command.

But thou wilt say that while they remain consubstantial with us, their dignity suffers from their submission to us.

And I say this to thee on this point, concerning the Only-Begotten: "If it were not written concerning Him that being in the form of God He counted it not a prize to be on an equality with God, but emptied Himself, taking the form of a servant, and being found in fashion as a man, He humbled Himself,----the form of thy objection might really have had a not invalid significance: but since the manner of His submission and humiliation is clear, why dost thou recklessly rail at Him Who endured to suffer even this for our sakes?" Making therefore our argument on every side to conform to accuracy of doctrine, we maintain that our Lord Jesus Christ has spoken the words of the phrase before us in full agreement with the scheme of His Incarnation.