Jesus died on the cross for you because He was God’s substitute for you.
He took your place by dying the sort of death you would have had to die if you had been left with the guilt of your sin. God set Him up as a substitute for you. He took the rap for you.
He died so that you would never have to die in that way (as someone who was being judged). But since Jesus has in fact died for you in that way, then you can say that you have died for your sin. You have died IN HIM.
In Christ, you have died for your sin.
In Christ, you have had your sin judged. In Christ, you have perfectly kept the law. In Christ, you have been justified.
In Christ, you now are able to obey Him (if you really want to).
In Christ, you now have a new life—His life in you.
God accepts you because He has placed you in Christ. He accepts His Son—so He accepts you! He loves His Son—so He loves you. He does not see His Son as being guilty—so He does not see you as being guilty. If you are a genuine Christian, then you are in Him.
Can you see that God’s acceptance of you really has nothing to do with you at all? It has nothing to do with what you are, or have done, or what you do or don’t do now. It is all to do with who Christ is, and what He has done. In other words, God deals with us only by dealing with Christ.
So then, God has done what you could never have done of yourself. He has once and for all dealt with your sin and your guilt and your disobedience and your failures and your angers and your resentments and your pride and your lusts, and everything else that makes you dirty to Him. He has taken it all away through His wonderful Son, Jesus Christ, and He accepts you totally as you are only because of who and what you are in Christ.
God has done all this only because He loves you. He has not done it because you were worthy of it or merited it. God the Father loved you enough to give up His Son to die on the cross for you. And Jesus loved you enough to voluntarily give Himself up to death for you. Read carefully John 3:16-18.
His love was such that He laid down His life on your behalf so that you would never have to bear the guilt and penalty of your sin or have to come under the wrath and condemnation of God due to your terrible disobedience. His love was such that He took onto His own shoulders all of your sin and guilt and penalty, and He suffered what you would have suffered of God’s wrath and judgement.
There is therefore now nothing of your past failure, present failure or future failure, which He did not carry away on that cross. He really has set you free!
Another terrific thing that Paul tells us in this verse 20 is that if we are believers, our life now has Christ’s life operating in us. The Bible tells us that when we become Christians, God gives us the gift of His Spirit. He comes to dwell in us. But that Spirit is the Spirit of Christ. It is He who comes and dwells in us. And He does this so that His life may be lived out through us.
Paul says in this verse, ‘the life I now live... I live by faith in the Son of God ‘. In other words, he trusts moment by moment that Christ will be working out His life in him. Paul knows that he has no ability of his own to live as a Christian in obedience to God. He will always fail if it’s left to him!
The same is true of you. You, of yourself, cannot live as a Christian. You will only ever live as God intended when by faith you trust Christ to live out His life in you and through you.
Actually, it is His faith not yours. You must learn to live by His faith, not your own. You must totally depend on Him or you will fall flat on your face! (I suspect that you must have already discovered that by now!)
Finally, Paul says in verse 21 that if justification can be achieved law-way, then Christ’s death was a waste of time. If you can be accepted by God through your observance of some law or rule or regulation, then there was no need for Christ to have died in the first place. He died to no purpose. As it is, you can’t be justified law-way, and so it can only happen as a result of God’s grace.
Paul’s strong stand on this great truth, and his insistence that nothing be added to what Christ has done, only enhances the wonderful fact that salvation is all of God’s grace. It is all of God’s goodness and free mercy and love. We contribute nothing to our salvation.