Hilary of Poitiers
Catena Aurea · Johannesevangelium 14
I will not leave you comfortless: I will come to you. Yet a little while, and the world seeth me no more: but ye see me: because I live, ye shall live also. At that day ye shall know that I am in my Father, and ye in me, and I in you. He that hath my commandments, and keepeth them, he it is that loveth me: and he that loveth me shall be loved of my Father, and I will love him, and will manifest myself to him. Because I live, ye shall live also.
(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)