John 7:17

One speaks in one way of the truth, in another way the truth interprets itself. The guessing at truth is one thing, and truth itself is another. Resemblance is one thing, the thing itself is another. And the one results from learning and practice, the other from power and faith. For the teaching of piety is a gift, but faith is grace. "For by doing the will of God we know the will of God." "Open, then," says the Scripture, "the gates of righteousness; and I will enter in, and confess to the Lord." But the paths to righteousness (since God saves in many ways, for He is good) are many and various, and lead to the Lord's way and gate. And if you ask the royal and true entrance, you will hear, "This is the gate of the Lord, the righteous shall enter in by it." While there are many gates open, that in righteousness is in Christ, by which all the blessed enter, and direct their steps in the sanctity of knowledge.

How then did the Lord answer those that were marvelling how He knew letters which He had not learned? "My doctrine," saith He, "is not mine, but His that sent me." This is the first profundity. For He seems as if in a few words He had spoken contraries. For He says not, This doctrine is not mine; but, "My doctrine is not mine." If not Thine, how Thine? If Thine, how not Thine? For Thou sayest both: both, "my doctrine;" and, "not mine." For if He had said, This doctrine is not mine, there would have been no question. But now, brethren, in the first place, consider well the question, and so in due order expect the solution. For he who sees not the question proposed, how can he understand what is expounded? The subject of inquiry, then, is that which He says, "My, not mine" this appears to be contrary; how "my," how "not mine"? If we carefully look at what the holy evangelist himself says in the beginning of his Gospel, "In the beginning was the Word, and the Word was with God, and the Word was God;" thence hangs the solution of this question. What then is the doctrine of the Father, but the Father's Word? Therefore, Christ Himself is the doctrine of the Father, if He is the Word of the Father. But since the Word cannot be of none, but of some one, He said both "His doctrine," namely, Himself, and also, "not His own," because He is the Word of the Father. For what is so much "Thine" as Thyself? And what so much not Thine as Thyself, if that Thou art is of another? The Word then is God; and it is also the Word of a stable, unchangeable doctrine, not such as can be sounded by syllables and fleeting, but abiding with the Father, to which abiding doctrine let us be converted, being admonished by the transitory sounds of the voice. For that which is transitory does not so admonish us as to call us to transitory things. We are admonished to love God. […]

(Tract. xxix. s. 3) Mine is not mine, appears a contradiction; why did He not say, This doctrine is not Mine? Because the doctrine of the Father being the Word of the Father, and Christ Himself being that Word, Christ Himself is the doctrine of the Father. And therefore He calls the doctrine both His own, and the Father's. A word must be a word of some one's. What is so much Thine as Thou, and what is so much not Thine as Thou, if what Thou art, Thou art of another. His saying then, My doctrine is not Mine own, seems briefly to express the truth, that He is not from Himself; it refutes the Sabellian heresy, which dares to assert that the Son is the same as the Father, there being only two names for one thing. (de Trin. i. c. xi) Or thus: In one sense He calls it His, in another sense not His; according to the form of the Godhead His, according to the form of the servant not His. (Tract. xxix. s. 6) Should any one however not understand this, let him hear the advice which immediately follows from our Lord: If any man will do His will, he shall know of the doctrine, whether it be of God, or whether I speak of Myself. What meaneth this, If any man will do His will? To do His will is to believe on Him, as He Himself says, This is the work of God, that ye believe on Him whom He hath sent. (c. 6:29) And who does not know, that to work the work of God, is to do His will? To know is to understand. Do not then seek to understand in order to believe, but believe in order to understand, for, Except ye believe, ye shall not understand. (Is. 7:9. Vulg.)

"If any man will do His will, he shall know of the doctrine, whether it be of God, or whether I speak of Myself." What He saith is this, "Cast out from yourselves the malice and wrath and envy and hatred which has without cause been conceived against Me, then there is nothing to hinder you from knowing that My words are indeed the words of God. For at present these things cast a darkness over you, and destroy the light of right judgment, while if ye remove them this shall no longer be your case." Yet He spake not (plainly) thus, (for so He would have confounded them exceedingly,) but implied it all by saying, "He that doeth His will shall know of the doctrine, whether it is of God, or whether I speak of Myself"; that is, "whether I speak anything different and strange and contrary to God." For, "of Myself" is always put with this meaning, that "I say nothing except what seemeth good to Him, but all that the Father willeth, I will also."

"If any man do His will, he shall know of the doctrine." What meaneth, "If any man do His will?" "If any man be a lover of the life which is according to virtue, he shall know the power of the sayings." "If any man will give heed to the prophecies, to see whether I speak according to them or not."