What spiritual effect will the doctrine of justification by faith have in the believer's life?
I think the main effect will be one of tremendous joy. It's a wonderful thing to wake up each day and realize that, although I'm an unworthy sinner, nevertheless, I am accepted in Christ. Further, I don't have to work for my acceptance. Life is not about keeping God happy by performance. It gives me enormous joy to know that the most important person in the universe accepts me as I am because of the merits of Jesus Christ credited to me.
Again, it's an amazing relief to know that God has dealt with all my sins and faults. He's taken my guilt away. I am accepted in Christ. I know that if I was to die tonight, I would go to be with my Lord in heaven.
Furthermore, now that I know that I'm saved through trusting Christ, I don't have to be terrified of the threat of Purgatory. I don't have any worries about whether people will pray for me after I die, or whether they'll light candles for me. Nor do I have to worry about whether my friends and relatives will pay to have masses offered for me after my death. Justification through faith deals with these and many other fears.
What will happen if the church loses the doctrine of justification by faith?
The first thing that will happen is that the Church will no longer have a gospel to declare. There will be no good news.
Second, believers will lose their sense of assurance. We will wonder if we have ever done enough to please God. “Are we good enough?” we will ask. On the other hand, if we believe this doctrine, it will have a significant impact on our lives. First, we will have peace with God. This means that we will be able to approach God as a friend. Second, it also means that we will have a totally different attitude to sin. When I think of all that God has done for me in Christ, I should hate sin with all my heart. When I reflect on what it cost the Son of God—damnation upon the cross, punishment in body, mind and spirit—I should loathe sin with every part of my being. When I know that I have been justified by grace through faith, I should delight in obeying the One who loved me and gave himself for me.