The apostle Paul cried out, “Who will rescue me from this body of death?” and answered his own question with a joyful prayer, “Thanks be to God—through Jesus Christ our Lord!” He was proclaiming the fact that God set us free from this body of death when he sent His Son for our salvation.
Old Testament saints such as the writer of Psalm 119 expressed similar joy, only then it was a forward-looking hope: “My soul faints with longing for your salvation, but I have put my hope in your word " Psalm 119:8. When he receives by faith the salvation he longed for God sets him free by changing his heart so he writes, “I run in the path of your commands, for you have set my heart free.” Psalm 119:32. When God sets our hearts free, we want nothing more than to obey Him. We delight ourselves in the Lord.
Why then do we still experience struggles such as Paul described – he doesn’t do what he wants to do and he does what he hates? It’s because, when Christ saved you, you were made new, but you are still you. If you were trying to live without God for any amount of time before He saved you, your sin nature was being formed in ways that are unique to you alone. The apostle Paul refers to this as the “old self,” which is still hanging around, fighting against the “new self.” Eph 4:22-24. But be of good cheer, God knows you better then you know yourself. You were his workmanship even before you were saved, he isn’t finished with you yet, and now that you know Him and can see His hand at work in your life you already have the victory. God is changing you into the image of Christ, and that is the best thing for you in the whole world.