2 Samuel 24:17

And how is it possible (you say) that one should so love his neighbor as himself? If others had not done this, you might well think it impossible: but if they have done it, it is plain that from indolence it is not done by ourselves. And besides, Christ enjoins nothing impossible, seeing that many have even gone beyond His commands. Who has done this? Paul, Peter, all the company of the Saints. Nay, indeed if I say that they loved their neighbors, I say no great matter: they so loved their enemies as no man would love those who were likeminded with himself. For who would choose for the sake of those likeminded, to go away into Hell, when he was about to depart unto a kingdom? No man. But Paul chose this for the sake of his enemies, for those who stoned him, those who scourged him. What pardon then will there be for us, what excuse, if we shall not show towards our friends even the very smallest portion of that love which Paul showed towards his enemies? And before him too, the blessed Moses was willing to be blotted out of God's book for the sake of his enemies who had stoned him. David also when he saw those who had stood up against him slain, saith, "I, the shepherd, have sinned, but these, what have they done?" And when he had Saul in his hands, he would not slay him, but saved him; and this when he himself would be in danger. But if these things were done under the Old [Covenant] what excuse shall we have who live under the New, and do not attain even to the same measure with them? For if, "unless our righteousness exceed that of the Scribes and Pharisees, we shall not enter into the kingdom of Heaven," how shall we enter in when we have even less than they?