My impression is that the epistles were written to folk among the Christian churches, who are being exhorted that faith is important to God. But I don’t think our tradition’s assumption is unreasonable that the value God places here on a trusting allegiance toward Him has relevance for those outside the church as well.
And on how God regards Good Samaritans, I wouldn’t assume that God doesn’t see an expression of “faith” in the reality of God’s goodness in many of the good deeds done by those who don’t believe in our particular Christian dogmas (I sense that the role Jesus’ story places the Samaritan in, convey a strong affirmation of him). But I’m content to let God evaluate each of us and whether we display a genuine definition of faith or not.
The main thing here for me is encouragement to personally trust in God and that genuine reward comes when I am faithful, which I do experience to be the case.