John Chrysostom
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.
(Hom. lxxxii) For there is no scandal so great as division, whereas unity amongst believers is a great argument for believing; as He said at the beginning of His discourse, By this shall all men know that ye are My disciples, if ye have love one to another. For if they quarrel, they will not be looked on as the disciples of a peacemaking Master. And I, He saith, not being a peacemaker, they will not acknowledge Me as sent from God.