Romans 4:5

However, to the one who does not work but trusts God who justifies the ungodly, their faith is credited as righteousness.

(v5, NIV)

Now the Paul begins to address the issue of faith. This is contrasted with "work". Instead of being one who works, Paul uses the example of one who trusts God. This trust in God is trust that God justifies the ungodly. Clearly Paul has already addressed the fact that all have sinned and fall short of the glory of God. All of us are ungodly. This trust in God of this person Paul describes is credited to him or her as righteousness. Instead of an owing of wages associated with work, there is a crediting as a result of faith.