Sanctification by the Spirit (Galatians 3:3-5).
In these verses, Paul moves on from the issue of our justification (based on Christ's imputed righteousness) to our sanctification (based on Christ's imparted righteousness).
We describe the nature of sanctification, and why we can only really be made perfect, through the nature of Christ being formed in us by the Holy Spirit, who is in us.
Our justification is a work of grace accomplished for us and received by faith in Christ.
Likewise, our sanctification is a work of grace accomplished in us through our faith in Christ, who continually supplies the Holy Spirit to us.
Paul says that trying to perfect oneself by doing the works of law, is fleshly and bound to fail, for if the flesh was impotent to justify us, why do we think it can sanctify us?
We can only experience God's life, blessing and be made perfect by grace through faith, for "the righteous by faith shall receive life and live by faith."
Although we have to cooperate with God in our sanctification, it is not by doing the works of the law, but by working out the salvation that God has worked within us by His Spirit.
The difference between sanctification by the flesh, doing works of law, and sanctification by the Spirit through the hearing of faith, is like the difference between rowing and sailing.
We have to stop trying and start trusting, and then obey as the Spirit leads us.
When we try to make ourselves perfect by the flesh, we are just imitating the Christian life,
rather than living from the reality of Christ's life within us, who perfects us by His Spirit of grace, as we trust and obey.