Paul quotes from Habakkuk 2:4 to support his claim that justification is by faith and not by obedience to the law.1 Quoting from one of the old covenant prophets, he is showing that this was the case (justification by faith) also in the time of the old covenant. It was always God’s plan.
11 Et que nul ne soit justifié devant Dieu par la loi, cela est évident, puisqu'il est dit: Le juste vivra par la foi.