When the Jews, upon the conviction of their sin, were cut to the heart, and cried out, ‘What shall we do?’ (Acts 2:37), what does Peter direct them to do? Does he bid them go and mortify their pride, wrath, malice, cruelty, and the like? No: he knew that was not their present work, but he calls them to conversion and faith in Christ in general, verse 38. Let the soul be first thoroughly converted, and then, 'looking on Him whom they have pierced’ (Zech. 12:10; John 19:37), humiliation and mortification will ensue….
[Jesus] tells us, ‘Make the tree good, and his fruit will be good’ (Matt. 12:33). The root must be dealt with, the nature of the tree changed, or no good fruit will be brought forth.
This is that I aim at: unless a man be regenerate, unless he be a believer, all attempts that he can make for mortification, be they never so specious [hallow or false] and promising—all means he can use, let him follow them with never so much diligence, earnestness, watchfulness, and intention of mind and spirit—are to no purpose. In vain shall he use many remedies: he shall not be healed.
… he sets himself to mortify the sin that galls him—which is a pure issue of self-love, to be freed from his trouble, and not at all to the work he is called unto—and so is diverted from it.
They set themselves to a relinquishment of sin, but not in that manner, by universal conversion, as God called for it. Thus are men diverted from coming unto God by the most glorious ways that they can fix upon to come to him by. And this is one of the most common deceits whereby men ruin their souls.”
(John Owen, Doctrine of Conversion, Not Repentance, for the Unbeliever. My emphasis added.)