The following is a Greek word commentary, taken from Wuest Word Studies – K. S. Wuest, on Galatians 2:20
I am crucified with Christ. The verb is in the perfect tense which speaks of a past completed action having present finished results. Paul uses it to show that his identification with Christ at the Cross was a past fact, and that the spiritual benefits that have come to him through his identification are present realities with him. By this statement he also shows how he died to the law, namely by dying with Christ who died under its penalty. The law’s demands were satisfied and therefore have no more hold on Paul. But thus being crucified with Christ, meant also to Paul, death to self. When Paul died with Christ, it was the Pharisee Saul who died. What he was and did up to that time passed away so far as he was concerned Saul was buried, and the old life with him. The dominating control of the Adamic nature had its power over him broken.
Nevertheless I live. Saul the self-righteous Pharisee, died, but Paul the great apostle, lives. The ego remained.
Yet not I, but Christ liveth in me. It is no longer a self-centered life that he lives, but a Christ-centered one. His new life is a Person, the Lord Jesus living in Paul. And through the ministry of the Holy Spirit. the Lord Jesus is manifest in his life. The new life is no longer, like the former one, dependent upon the ineffectual efforts of a man attempting to draw near to God in his own righteousness. The new life is a Person within a person, living out His life in that person. Instead of attempting to live his life in obedience to a set of rules in the form of the legal enactments of the Mosaic law, Paul now yields to the indwelling Holy Spirit and cooperates with Him in the production of a life pleasing to God, energized by the divine life resident in him through the regenerating work of the Spirit. Instead of a sinner with a totally depraved nature attempting to find acceptance with God by attempted obedience to a set of outward laws, it is now the saint living his life on a new principle, that of the indwelling Holy Spirit manifesting forth the Lord Jesus. That is what Paul means when he says: And the life which I now live in the flesh, I live by the faith of the Son of God, who loved me and gave Himself for me.
Translation. With Christ I have been crucified, and it is no longer I who live, but there lives in me Christ. And that life which now I live in the sphere of the flesh, by faith I live it, which faith is in the Son of God who loved me and gave Himself on my behalf.