Before Christianity, which is the full revelation of God, there were indeed, as need not be said, souls born anew; but their rule, when a rule was definitely given, was man's responsibility (whatever piety and grace might inspire), and the law, which was the perfect measure of that which man, as a being responsible to God, ought to be. Saints then did not distinguish between a new and an old man, although of necessity they had the conscience of the old man and the tastes of the new in measure in many respects. The sense, for instance, of the evil of falsehood had not at all the same place as with the Christian. Now the new man is renewed in knowledge after the image of Him who created him. God Himself in His nature is the standard of good and evil, because the new man has the knowledge of what that nature is: he is made a partaker of it, and he has the light of God. It is an intelligent participation by grace in the nature of God, which is the marvelous and precious privilege of the Christian. God works in this nature; but by communicating it He has placed man in this position. Christ is the perfect model of this image, the type of the new man.
Other differences have disappeared: there remains but the old man, which we only acknowledge as dead, and the new man. [emphasis added]
(J. N. Darby, Synopsis of the Books of the Bible, Volume 5, last checked 2015-09-11)