Gal 2:17-21

Now, after my previous post on justification and righteousness let's finish off chapter 2 with this final paragraph.

Paul has been writing, vv. 15-16, that in Christ we are already justified (made right with God). But, we know, at least I hope we do, that in our lives we continue to sin. This appears a serious objection to Paul's understanding of justification. If we sin how can we be justified, does justification become a hope stored up for us in glory? Or, if we sin does that make Christ, to whom we are united, a sinner or servant of sin? 'Certainly not!' isn't really strong enough for Paul's rejection of this error.

Christ dies for us and God accepts the sacrifice of Christ on our behalf. On this basis alone we are justified, made righteous before God.
This is what God, through Christ, has done for us.

I however, continue to live in sin. V. 18 is a very vivid picture of my rebuilding walls of sin which Christ has torn down. Christ destroys sin, if it is rebuilt or continues in my life that is up to me.
Why do we continue to sin?

Paul seeks to address our minds, our understanding of who we now are in Christ.
v. 19 - if I have died to the law I am no longer bound to the law but am set free to live to God.
v. 20 - on the cross Christ died to sin and rose again to a new life. United to Christ, 'in Christ', I share in his death to sin and also share in his rising to a new life. Everyday I live now, I live as one united to the Son of God and sharing his life, or knowing his life powerfully within me.
These verses describe a change, a change that has taken place within us. We can choose, it would appear every day, whether we will slip back into the old life or vigorously enter into the new life. In the weakness of our flesh (to use a loaded Pauline term!) we cannot but fail to live this new life and constantly fall back into the old life of sin and death.
This does not in any way diminish the reality, the fact of the cross and what God has achieved for us in Christ. This does not allow us to settle for sin and condone sin, rather we are to 'endeavour' (v. 17) to live in Christ, to enjoy the new life of those justified, made right with God through the cross of the Lord Jesus.
How can we encourage ourselves and others to live as those already justified? What role does faith play in this?