There are many things about the Christian faith that are hard to believe. But one of the most challenging is our view of the relationship between faith and works.
Every religion with some kind of concept of sin has to address how to be seen as just, or righteous, in the eyes of God. Maybe a simpler way to explain it is with this question: How can we make up for our sins? And these religions usually come to the same conclusion: The key to righteousness is some kind of combination of faith and works, with the latter usually having a greater emphasis than the former. Beliefs may matter, but deeds matter more.
And then there’s what Christians believe. We believe what we do matters, of course; but we don’t see our works as a means of earning God’s favor. There’s no way for us to offset the offense of our sin against a perfect and holy God. God’s favor comes to us one way, and one way alone: through faith in Jesus Christ, the only truly righteous Person, the only Person who perfectly obeyed God in every way (Rom. 8:33-34; Eph. 2:8-9). That’s the heart of what Christians mean by the term justification by faith. Righteousness, or justification, is something none of us can earn but is freely given to all who trust in Christ. And through our justification, we are pardoned and declared to be in right standing before God, no longer estranged but adopted into His family.