How the just live

Habakkuk mentioned it first.  He was looking into the future.  The "just shall live by faith" (Hab 2:4) 
Since no one is righteous, how can this be true?  Christ came so that the unjust could be "just". (1 Peter 3:18). Paul makes mention of the righteous living by faith throughout Romans.  In the first chapter he quotes from Habakkuk.
Rom. 1:17 For in it the righteousness of God is revealed from faith to faith, just as it is written: The righteous will live by faith.
Two chapters later, he makes the application of what Christ's work has accomplished for everyone who believes. God presented him to demonstrate his righteousness at the present time, so that he would be just and justify the one who has faith in Jesus. (Rom. 3:26). Praise God!