John 14:20

(viii. de Trin) Or He means by this, that whereas He was in the Father by the nature of His divinity, and we in Him by means of His birth in the flesh; He on the other hand should be believed to be in us by the mystery of the Sacrament: as He Himself testified above: Whoso eateth My flesh, and drinketh My blood, dwelleth in Me, and I in Him. (supr. 6:54)

(Hom. lxxv. 2) Or, in that day, on which I shall rise again, ye shall know. For His resurrection it was that established their faith. Then the powerful teaching of the Holy Spirit began. His saying, I am in the Father, expresses His humility; the next, And ye in Me, and I in you, His humanity and God's assistance to Him. Scripture often uses the same words in different senses, as applied to God and to men.

"In that day," He says, "ye shall know that I am in my Father, and ye in me, and I in you." In what day, but in that whereof He said, "Ye shall live also"? For then will it be that we can see what we believe. For even now is He in us, and we in Him: this we believe now, but then shall we also know it; although what we know even now by faith, we shall know then by actual vision. For as long as we are in the body, as it now is, to wit, corruptible, and encumbering to the soul, we live at a distance from the Lord; for we walk by faith, not by sight. Then accordingly it will be by sight, for we shall see Him as He is. For if Christ were not even now in us, the apostle would not say, "And if Christ be in you, the body is dead indeed because of sin; but the spirit is life because of righteousness." But that we are also in Him even then, He makes sufficiently clear, when He says, "I am the vine, ye are the branches." Accordingly in that day, when we shall be living the life, whereby death shall be swallowed up, we shall know that He is in the Father, and we in Him, and He in us; for then shall be completed that very state which is already in the present begun by Him, that He should be in us, and we in Him.

It follows: In that day (the day of which He saith, ye shall live also) ye shall know, i. e. whereas now ye believe, then ye shall see, that I am in the Father, and ye in Me, and I in you. For when we shall have attained to that life in which death is swallowed up, then shall be finished that which is now begun by Him, that He should be in us, and we in Him.

By love, and the observance of His commandments, that will be perfected in us which He has begun, viz. that we should be in Him, and He in us. And that this blessedness may be understood to be promised to all, not to the Apostles only, He adds, He that hath My commandments and keepeth them, he it is that loveth Me.