John Calvin on John 15:17

17. These things I command you. This too, was appropriately added, that the Apostles might know that mutual love among ministers is demanded above all things, that they may be employed, with one accord, in building up the Church of God; for there is no greater hindrance than when every one labors apart, and when all do not direct their exertions to the common good. If, then, ministers do not maintain brotherly intercourse with each other, they may possibly erect some large heaps, but latterly disjointed and confused; and, all the while, there will be no building of a Church.