A.(19) For I through the law am dead to the law,
B. that I might live unto God.
C.(20) I am crucified with Christ:
D. nevertheless I live;
E. yet not I, but Christ liveth in me:
D’. and the life which I now live in the flesh
C’. I live by the faith of the Son of God, who loved me, and gave himself for me.
B’.(21) I do not frustrate the grace of God:
A’. for if righteousness come by the law, then Christ is dead in vain.
I get slightly different pairings from NASB95:
19 “For through the Law I died to the Law,
so that I might live to God.
……20 “I have been crucified with Christ;
…………and it is no longer I who live,
…………but Christ lives in me;
………………and the [life] which I now live in the flesh
………………I live by faith in the Son of God,
…………who loved me
…………and gave Himself up for me.
……21 “I do not nullify the grace of God,
for if righteousness [comes] through the Law,
then Christ died needlessly.”