We know without doubt that salvation is a gift from God given on the basis of grace through faith and not works (Eph 2:8-9). Scripture is quite clear that we are justified by faith apart from works (Rom 3:28; Gal 2:16; Rom 3:20). It is, in fact, one of the largest distinctives of Christianity. Every other religion operates on a works basis -- be good and you get rewarded with a good hereafter. Christianity alone starts with the premise "There is none righteous; no, not one." (Rom 3:10)
So ours is a faith-based religion; the question is one of faith alone. "Do you have faith in Christ?" is the sole question to ask. And if the person responds, "Yes," well, then, you had better not question their status. Because ours is a faith-based religion, not works.
As it turns out, however, the Bible teaches something different. Mere faith is not what it takes to be saved. There are, as it turns out, two kinds of faith.
You can see the two in Jesus's parable of the sower (Matt 13:3-9) and, of course, His explanation of it (Matt 13:18-23). In this story there are four types of "ground". The first is hard and the seed doesn't penetrate. The second is rocky and the seed grows but dies immediately. The third is thorny and the seed grows but is choked out by weeds. The fourth is "good soil" where the seed grows and produces grain. In Jesus's explanation, the first kind never penetrates and the last kind is genuine saving faith, but the other two are not. It must be noted, however, that these do have some sort of faith. The "rocky ground" "receives it with joy". That's a kind of faith. And the thorny ground also shoots up growth, but is choked out. This, too, is some kind of faith. Neither of these, however, is a kind of faith that saves.
Of course, James is less ambiguous. "What good is it, my brothers, if someone says he has faith but does not have works? Can that faith save him?" (James 2:14) We would call that "profession, not possession of faith", but James refers to it as "faith". He says that faith that produces no works is "dead" (James 2:17). James argues that verbal faith is one thing and a faith that produces works is another (James 2:18). There is, then, a living, saving faith and a dead faith. Dead faith does not save.
We see the same thing in Jesus's story of the sheep and the goats (Matt 25:31-46). We know that the sheep entered eternal life and the goats went to eternal punishment (Matt 25:46). What was the difference? Wait! Don't jump to conclusions. The difference was that sheep are sheep and goats are goats. The difference is what they were. However, this difference was highlighted by ... what they did. That is, sheep act one way and goats act another even if they might appear similar. As Jesus put it, "You will recognize them by their fruits." (Matt 7:16)
The Bible is full of the declaration that we are saved by faith apart from works. This cannot be doubted. The Bible is just as clear, however, that living, saving faith produces works. We are saved by faith apart from works, but not a faith that does not produce works. The faith that saves certainly produces obedience -- what Paul terms "the obedience of faith" (Rom 1:5; Rom 16:26). John says that it is impossible for a person genuinely born of God to make a practice of sin (1 John 3:9). So, yes, we are saved not by works, but by faith. Don't be confused, however. A faith that produces no works is a dead faith and cannot save. Paul says, "Examine yourselves, to see whether you are in the faith. Test yourselves. Or do you not realize this about yourselves, that Jesus Christ is in you?" (2 Cor 13:5) "Christ in you" cannot fail to produce a changed life. Don't be deceived into dead faith.