Augustine of Hippo
Catena Aurea · Johannesevangelium 17
Neither pray I for these alone, 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: I in them, and thou in me, that they may be made perfect in one: and that the world may know that thou hast sent me, and hast loved them, as thou hast loved me.
(Tr. cx) But why does He say, That the world may believe that Thou hast sent Me? Will the world believe when we shall all be one in the Father and the Son? Is not this unity that peace eternal, which is the reward of faith, rather than faith itself? For though in this life all of us who hold in the same common faith are one, yet even this unity is not a means to belief, but the consequence of it. What means then, That all may be one, that the world may believe? He prays for the world when He says, Neither pray I for these alone, but for all those who shall believe on Me through their word. Whereby it appears that He does not make this unity the cause of the world believing, but prays that the world may believe, as He prays that they all may be one. The meaning will be clearer if we always put in the word ask; I ask that they all may be one; I ask that they may be one in Us; I ask that the world may believe that Thou hast sent Me.