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.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: Hom. lxxxii