Amen and justified means 'right', so we are right ('dikios' in the Greek) in God's sight by faith in Jesus Christ. It feels good to be on God's good side by simple child like faith in him. It's an allegiance thing, your giving your allegiance to the King of kings Lord of lords, and God honors that and commits himself to you for ever, makes you his child, gives you all things, makes you a new creation.