Visible unity among believers serves the world's recognition of Jesus' mission.

John 17:21–23

²¹That 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.

²²And the glory which thou gavest me I have given them; that they may be one, even as we are one:

²³I 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.