Love all men, even your enemies; love them, not because they are your brothers, but that they may become your brothers. Thus you will ever burn with fraternal love, both for him who is already your brother and for your enemy, that he may by loving become your brother. … Even he that does not as yet believe in Christ … love him, and love him with fraternal love. He is not yet thy brother, but love him precisely that he may be thy brother.

p.436 - On the Mystical Body of Christ