If there come any unto you, and bring not this doctrine, receive him not into your house, neither bid him God speed:
If there come any - as a teacher or brother: indicative, not subjunctive: implying that such persons do actually, and are sure to come: when any comes, as there will. True love is combined with hearty separation from all that is false, whether persons or doctrines. Misbelief destroys faith, the source of love, so love itself: therefore love abhors it as overthrowing Christianity, the center of love's affection.
Receive him not ... neither bid him God speed. This is not said of those always aliens from the Church, but of those who wish to be esteemed brethren, and subvert true doctrine (Grotius). The greeting forbidden in the case of such is that usual among Christian brethren: not a mere formality, but a token of Christian brotherhood.