The Gospel has power to save because it reveals righteousness. This righteousness is “from faith to faith” or we might say “is all about faith”. In other words, you can’t add anything such as works to faith in order to gain righteousness. Paul quotes Habakkuk 2:4 to back this up, “The righteous will live by faith.” There has been some discussion over the years about whether or not Paul’s usage of the quote fits with its original intent. Does “live by faith” mean that their new life comes as a result of faith, or that their righteous living is faithful living. I don’t think we need to over think this. At this point, Paul simply wants to draw our attention to the exclusive relationship between righteousness and faith. Habakkuk’s point may be more to do with how we live faithfully than how we are saved but Paul will want to draw a link between our life and salvation which means that if we are to know how to live the faithful life Habakkuk speaks of then we need to pay attention to what Paul says. Romans not only uses Habakkuk but helps us to interpret the prophecy more sharply (v17).
Righteousness is revealed because God’s wrath is revealed. It’s God’s wrath. We may not be comfortable with the idea of God being angry and it’s important not to confuse this settled will against evil with human loss of temper but we do need to recognise that it is there in the Bible. Moreover, Paul gives us a framework for viewing the world around us and events here. The passive voice is used wrath is revealed and that suggests that this is not something stated by God in Scripture or even by prophetic word but by General Revelation as we experience the consequences of the Fall. It’s from heaven, a reminder again that it is God’s judgement and it’s against human ungodliness and unrighteousness. Our ungodliness is seen in that we choose to supress truth. The idea is that God’s revelation of who he is and what goodness is, is not hidden, it’s obvious. It’s sinful men who try to supress it, to hide it from view to stop it. Notice that sin is two-fold. We both try to do evil and stop good (v18).
To be clear, it is not that God has been hiding, or even that humanity have been unable to see and to know him. God has revealed who he is to them (v19). Creation makes visible his invisible attributes so that humanity has no excuse for rejecting God, it is an active decision of the will in the face of contrary and overwhelming evidence (v20). They knew God but chose not to honour him, not to glorify him in their worship. The result was that their reasoning was affected, the rejection of the light of his revelation meant that their hearts were darkened and their reasoning futile (v21). We want to believe that we are wise and clever but rejecting God shows us to be foolish (v22). Humans were made in God’s image to worship God but we choose to exchange the creator’s image for the images of creation. This I think means both that we choose to be less than what we are, we reject being his image bearers but also that we choose to worship idols, images that we have made for ourselves inspired by creation (v23).