John 10:38

(vii. de Trin. 26) What place hath adoption, or the mere conception of a name then, that we should not believe Him to be the Son of God by nature, when He tells us to believe Him to be the Son of God, because the Father's nature showed itself in Him by His works? A creature is not equal and like to God: no other nature has power comparable to the divine. He declares that He is carrying on not His own work, but the Father's, lest in the greatness of the works, the nativity of His nature be forgotten. And as under the sacrament of the assumption of a human body in the womb of Mary, the Son of God was not discerned, this must be gathered from His work; But if I do, though ye believe not Me, believe the works. Why doth the sacrament of a human birth hinder the understanding of the divine, when the divine birth accomplishes all its work by aid of the human? Then He tells them what they should gather from His works; That ye may know and believe, that the Father is in Me, and I in Him. The same declaration again, I am the Son of God: I and the Father are one.

(Tract. xlviii. 10) The Son doth not say, The Father is in Me, and I in Him, in the sense in which men who think and act aright may say the like; meaning that they partake of God's grace, and are enlightened by His Spirit. The Only-begotten Son of God is in the Father, and the Father in Him, as an equal in an equal.

"If I do not the works of my Father, believe me not. But if I do, though ye will not believe me, believe the works; that ye may know and believe that the Father is in me, and I in Him." The Son says not, "the Father is in me, and I in Him," as men can say it. For if we think well, we are in God; and if we live well, God is in us: believers, by participating in His grace, and being illuminated by Himself, are in Him, and He in us. But not so is it with the only-begotten Son: He is in the Father, and the Father in Him; as one who is equal is in him whose equal he is. Recognize the prerogative of the Lord, and the privilege of the servant. The prerogative of the Lord is equality with the Father: the privilege of the servant is fellowship with the Saviour.

What He saith is of this kind: "If those who have received this honor by grace, are not found fault with for calling themselves gods, how can He who hath this by nature deserve to be rebuked?" Yet He spake not so, but proved it at a later time, having first relaxed and yielded somewhat in His discourse, and said, "Whom the Father hath sanctified and sent." And when He had softened their anger, He bringeth forward the plain assertion. For a while, that His speech might be received, He spoke in a humbler strain, but afterwards He raised it higher, saying, "If I do not the works of My Father, believe Me not; but if I do, though ye believe not Me, believe the works." Seest thou how He proveth what I said, that He is in nothing inferior to the Father, but in every way equal to Him? For since it was impossible to see His Essence, from the equality and sameness of the works He affordeth a proof of unvaryingness as to Power. And what, tell me, shall we believe? "That I am in the Father, and the Father in Me." "For I am nothing other than what the Father is, yet still Son; He nothing other than what I am, yet still Father. And if any man know Me, he knoweth the Father, and if he knoweth the Father, he hath learnt also the Son." Now were the power inferior, then also what relateth to the knowledge would be false, for it is not possible to become acquainted with one substance or power by means of another.