On The Holy Trinity by St. Augustine
Chapter 8.--In What Manner Christ Wills that All Shall Be One in Himself.
12. So the Son of God Himself, the Word of God, Himself also the Mediator between God and men, the Son of man, equal to the Father through the unity of the Godhead, and partaker with us by the taking upon Him of humanity, interceding for us with the Father in that He was man, yet not concealing that He was God, one with the Father, among other things speaks thus: |Neither pray I for these alone,| He says, |but for them also which shall believe on me through their word; that they all may be one; as Thou, Father, art in me, and I in Thee, that they also may be one in us: that the world may believe that Thou hast sent me. And the glory which Thou gavest me I have given them; that they may be one, even as we are one.|