20. But ye have not. He now draws a contrast of a Christian life, so as to make it evident how utterly inconsistent it is with the character of a godly man to defile himself regardlessly with the abominations of the Gentiles. Because the Gentiles walk in darkness, therefore they do not distinguish between right and wrong; but those on whom the truth of God shines ought to live in a different manner. That those to whom the vanity of the senses is a rule of life, should yield themselves up to base lusts, is not surprising; but the doctrine of Christ teaches us to renounce our natural dispositions. He whose life differs not from that of unbelievers, has learned nothing of Christ; for the knowledge of Christ cannot be separated from the mortification of the flesh.