I agree with about 90% of this excerpt, taken from The Cost of Discipleship, but 100% of it makes me think:
What is undivided love? Love which shows no special favour to those who love us in return. When we love those who love us, our brethren, our nation, our friends, yes, and even our own congregation, we are no better than the heathen and publicans. Such love is ordinary and natural, and not distinctively Christian. We can love our kith and kin, our fellow-countrymen and our friends, whether we are Christians or not, and there is no need for Jesus to teach us that. But he takes that kind of love for granted, and in contrast asserts that we must love our enemies. Thus he shows us what he means by love, and the attitude we must display towards it.
How then do the disciples differ from the heathen? What does it really mean to be Christian? Here we meet the word that controls the whole chapter [Matthew 5], and sums up all we have heard so far. What makes the Christian different from other men is the “peculiar,” the Πξρισσον, the “extraordinary”…
The Πξρισσον never merges into the το αυτο. That was the fatal mistake of the false Protestant ethic which diluted Christian love into patriotism, loyalty to friends, and industriousness, which in short, perverted the better righteousness into justitia civilis. Not in such terms as these does Jesus speak. For him, the hall-mark of the Christian is the “extraordinary.” The Christian cannot live at the world’s level, because he must always remember the Πξρισσον.
What is the precise nature of the Πξρισσον? It is the life described int the beatitudes, the life of the followers of Jesus, the light which lights the world, the city set on the hill, the way of self-renunciation, of utter love, of absolute purity, truthfulness and meekness. It is unreserved love for our enemies, for the unloving and unloved, love for our religious, political and personal adversaries. In every case it is the love which was fulfilled in the cross of Jesus Christ himself, who went patiently and obediently to the cross–it is in fact the cross itself.