Follow Up #1: What is Faith?
The series on why I’m not a Roman Catholic despite the temptation to return to the Church was extremely brief. I oversimplified many issues, and I wanted to take a quick moment to hash out the ones that deserve further examination. Let’s start with what my wise brother-in-law pointed out in a comment to part #1, which is that a lot of what I said hinges on defining faith.
Authentic biblical faith has two prongs to it. The first is right belief, or “orthodoxy.”  Generally speaking, to call yourself a Christian you would have to adhere to the following minimalist set of beliefs:
- Existence of God as a Trinity
- Preeminence of Christ over his creation
- Mankind fell into sin, and is now utterly enslaved to it
- Death of Jesus making atonement for the sins of mankind
- Resurrection of Jesus on the third day
- Future return of Christ to judge the living and the dead
And the rest varies quite wildly, even the mechanics of the above vary somewhat (even if the generic belief is still the same).
You need more, because the devil believes that stuff too. The second prong is right practice, or “orthopraxy.”  Pure religion is to help others and stay separate from the rest of the world.
Again, it’s great if you save the world, either by donating money to causes, championing nonprofits, or rolling up your sleeves and building an orphanage. The rich young ruler told Jesus he kept all the commands from childhood, and he wanted to know what else he lacked. Jesus also told his disciples during the Sermon on the Mount that people who did a lot of great things will cry out for Jesus and he will tell them to depart into hell. Doing good isn’t enough, either.
You need to bring the two prongs together. Faith is neither one nor the other, but both together. Salvation occurs solely by grace, but we respond to that grace in faith. It’s not just believing. It’s not just acting on a belief. Mere belief and mere action are both condemned in Scripture. Both belief and action are required; one separate from the other isn’t going to cut it.
Saving faith always and necessarily produces works, but the works alone will never create a saving faith. Works apart from faith are merely some rote ceremony, performed without thought for the one whom the works are supposed to glorify. Faith apart from the works is similarly dead. What good is a belief until you act on it, after all?
J.P. Holding explains this in more detail here.
Therefore, a true saving faith is going to manifest itself in the life of the believer in a conspicuous way, through that believer’s works. We see this in the changed lives of those who surrender to Christ. 
- Christians have a variety of beliefs, and what should be categorized as orthodox (beyond what I’ve listed), apostasy, or heresy is beyond my scope here.
- Christians have a wide variety of practices. In general, I’m only considering the spirit of “true religion” passage in James 1:27; basically, helping those in need and staying set apart from the world so that the culture notices that you’re different.
- It is beyond the scope of this post to consider how we would know the difference between counterfeit faith in idols and authentic Christianity. For example, I’m not considering why prayer and meditation appear to produce the same results, nor how Scientology could save a drug addict from his addiction as effectively as Christianity. Suffice to say, I don’t consider that a valid argument against the truth claims of Christianity.