We don't know how to solve the root problem of the world.
1. Our problem is spiritual. The immorality, hypocrisy, no respect for God. Universal (v10). All have sinned (v23). All equally under the problem of sin, ie have rejected the leadership of God (v9, 19).
2. The solution - only one solution. (v21) God has acted to solve the problem. Jesus takes our place, so that If we put our trust in that, we are righteous before God. Four key words (b) Blood - Old Testament imagery (b) Redemption - pay the debt. (c) Justified - legal concept - declared non-guilty. (d) Faith - only applies by faith in Jesus Christ (v22).
3. The Cross from God's perspective. It demonstrates God's righteous. (v25,26). God's wrath is satisfied by the offering of Jesus (God provides the solution - He takes the anger on Himself). It is all about God and His glory.