Some of the elect are converted after their early years, having lived in the natural state for a time and served various evil desires and pleasures. God gives these repentance to life as part of their effectual calling (Tit 3:2-5).
There is no one who does good and does not sin (Ecc 7:20). Even the best may fall into great sins and offenses, through the power and deceitfulness of the corruption in them, along with the strength of temptation. Therefore, God has mercifully provided in the covenant of grace that believers who sin and fall will be renewed through repentance to salvation (Lk 22:31-32).
This saving repentance is a gospel grace (Zec 12:10; Ac 11:18) in which those who are made aware by the Holy Spirit of the many evils of their sin, by faith in Christ humble themselves for it with godly sorrow, hatred of it, and self-loathing (Eze 36:31; 2Co 7:11). They pray for pardon and strength of grace and determine and endeavor by provisions from the Spirit to live before God in a well-pleasing way in everything (Ps 119:6, 128).
Repentance must continue throughout our lives, because of the body of death and its activities. So it is everyone’s duty to repent of each specific, known sin specifically (Lk 19:8; 1Ti 1:13, 15).
God has made full provision through Christ in the covenant of grace to preserve believers in their salvation. Thus, although there is no sin so small that it is undeserving of damnation (Ro 6:23), yet there is no sin so great that it will bring damnation on those who repent (Isa 1:16-18; 55:7). This makes the constant preaching of repentance necessary.