There’s a good deal of oversimplification going on in this discussion.
The faith-alone idea comes from many passages like John 3:16:
For God so loved the world, that he gave his only Son, that whoever believes in him should not perish but have eternal life.
Once-saved-always-saved doesn’t make a lot of sense divorced from the entire complex of reform theology, which hinges on the idea of predestination. Romans has the strongest passages on this, as I’m sure the participants of this discussion know, and the reform guys decided they couldn’t throw out that 800-lb baby with the bathwater (to mix metaphors), just because the Bible also discusses the importance of faith and works.
The question is, What is the root cause of salvation? Yes, faith and works are important, but as signs of salvation or as causes? Calvin et al. decided that they are signs and not causes. The crux of the reason they go this way is that there are such problems with free will, which both the faith folks and the works wonks assume (and which y’all in the Catholic Church are sold on, as are most Protestant denominations).
In a nutshell, free will requires God to relinquish his sovereignty, passing measures of it to us buzzing little humans. Yes, yes… made in His image, etc. … I can argue for free will, too. But the reform radicals couldn’t stand the idea of us being a kind of minor deities and decided we must have been selected for salvation – or not selected. From this flows the idea of once-saved-always-saved. If God chose you, how can you unchoose you? One expects faith and works from someone chosen by God for salvation, but there’s no earnin’ nothin’ in this framework.
I know it’s hard to swallow, or even understand. My Presbyterian pastors (supposedly reform-based) haven’t bought it. But some of the greatest energy in the Protestant world right now is pure, old-time, hard-core Calvinist reform theology. Lots of young people, energetic gatherings, avid study.
Someone mentioned Jonathan Edwards. You can also read C. H. Spurgeon; the old rascal himself, John Calvin; and many modern reform writers like R. C. Sproul.