I'll be first to say, genuine believers are forgiven and will never perish. They have this gift not for any works they do, but through faith in what Christ has done for them. Moreover, his Spirit preserves them in faith to the end so that "not one is lost."
Because of this lavish grace, some presume wrongly that salvation belongs to unrepentant people or that we should hesitate to "snatch some from the fire" with a firm hand. It seems to contradict their understanding of the character of grace. However, "he who began a good work in you will finish it," also means Spirit-wrought repentance is present to the end of believers' lives. Sanctification doesn't save, but the grace that saves sanctifies.
Things get sticky when we try to say how God fosters this repentance. Many Protestants have forgotten (or now embrace) the errors we stood against during the Reformation. During that period the church attempted to scrub herself of a thousand years of false ideas and practices, errors that fastened on her hull like barnacles on a long voyage. We cleansed ourselves of Rome's subversion of Scripture as the supreme authority, and their rejection of salvation by grace alone through faith in Christ alone. Many of us forget, however, that we also protested medieval mystic and Anabaptist tendencies to deny God's use of ordinary means to accomplish his supernatural goals.
Many Protestants now believe God sanctifies believers regardless of our attending church, hearing teachers, being held accountable, praying, etc. We expect those in sin to be restored with minimal personal intervention. We have adopted a stance of practical pacifism in the spiritual war.
Of course God has power to work apart from means, just as he has power to flood the whole earth again. The question is, what has he said he will do? God bound himself never to send another similar flood; so he binds himself to certain means for the purpose of sanctifying the church. Primarily, he works through the Word and sacraments, and secondarily through his church as a living community. He uses accountability, exhortation, rebuke, and if necessary, church discipline.
The attitude of those who reject ordinary means is more gnostic than Christian. It is a rejection of the Body. After the attitude, "it's just me and my Bible," comes, "it's just me and my (unaccountable) experience." Then the sky's the limit. The work of reformation is never over. The barnacles come back. As you consider what it means to be a Protestant, know that it is as gnostically Anabaptist to deny practical means as part of God's work, as it is Roman superstition to think the means themselves guarantee or accomplish that work. We do as God commands us, trusting him to perform his will.