To mortify a sin is not utterly to kill, root it out, and destroy it, that it should have no more hold at all nor residence in our hearts. It is true this is that which is aimed at; but this is not in this life to be accomplished. There is no man that truly sets himself to mortify any sin, but he aims at, intends, desires its utter destruction, that it should leave neither root nor fruit in the heart or life. He would so kill it that it should never move nor stir any more, cry or call, seduce or tempt, to eternity. Its not-being is the thing aimed at.
Now, though doubtless there may, by the Spirit and grace of Christ, a wonderful success and eminency of victory against any sin be attained, so that a man may have almost constant triumph over it, yet an utter killing and destruction of it, that it should not be, is not in this life to be expected. This Paul assures us of, Phil. 3:12, “Not as though I had already attained, either were already perfect.” He was a choice saint, a pattern for believers, who, in faith and love, and all the fruits of the Spirit, had not his fellow in the world, and on that account ascribes perfection to himself in comparison of others, verse 15; yet he had not “attained,” he was not “perfect,” but was “following after:” still a vile body he had, and we have, that must be changed by the great power of Christ at last, verse 21. This we would have; but God sees it best for us that we should be complete in nothing in ourselves, that in all things we must be “complete in Christ;” which is best for us, Col. 2:10.
– John Owen –
from The Mortification of Sin in Believers, volume 6 of Works, pages 24-25