And have put on the new man, which is renewed in knowledge after the image of him that created him: And have put on the new man - See on Romans 12:1-2 (note).
Is renewed in knowledge - Ignorance was the grand characteristic of the heathen state; Knowledge, of the Christian. The utmost to which heathenism could pretend was a certain knowledge of nature. How far this went, and how much it fell short of the truth, may be seen in the writings of Aristotle and Pliny. Christianity reveals God himself, the author of nature; or, rather, God has revealed himself, in the Christian system with which he has blessed mankind. Christianity teaches a man the true knowledge both of himself and of God; but it is impossible to know one's self but in the light of God; the famous γνωθι σεαυτον, know thyself, was practicable only under the Christian religion.
After the image of him that created him - We have already seen that God made man in his own image; and we have seen in what that image consisted. See the notes on Genesis 1:26, and on Ephesians 4:23 (note), Ephesians 4:24 (note). Does not the apostle refer here to the case of an artist, who wishes to make a perfect resemblance of some exquisite form or person? God in this case is the artist, man is the copy, and God himself the original from which this copy is to be taken. Thus, then, man is made by his Creator, not according to the image or likeness of any other being, but according to his own; the image του Κτισαντος, of the Creator. And as the Divine nature cannot exist in forms or fashions, moral qualities alone are those which must be produced. Hence the apostle, interpreting the words of Moses, says that the image in which man was made, and in which he must be remade, ανακαινουμενον, made anew, consists in knowledge, righteousness, and true holiness.