Mankind is not justified before God by working hard to please Him. Paul simply says that if that were so, then Christ died in vain. Rather mankind is saved by the Work of God in His Son, Jesus Christ and by God’s Grace and Mercy.
Paul also says that if we fall into sin, that does not then make Christ the “minister of sin!” He also claims that if we strive to obey the Law, we make ourselves trespassers. Rather we “are fixed to the Cross” so as “to live to God with Christ.” The Law is nailed there on the tree, and all its power destroyed.
Paul warns “cast not away the Grace of God.”
“16 know that a man [soothly knowing for a man] is not justified of the works of the law, but by the faith of Jesus Christ; and we believe in Jesus Christ, that we be justified of the faith of Christ [that we be justified by the faith of Christ], and not of the works of the law. Wherefore of the works of the law each flesh shall not be justified.
17 And if we seek to be justified in Christ, we ourselves be found sinful men, whether Christ be minister of sin? God forbid. [That if we seeking to be justified in Christ, and we ourselves be found sinners, whether Christ is minister of sin? Far be it.]
18 And if I build again things that I have destroyed [Soothly if I build again those things that I destroyed], I make myself a trespasser.
19 For by the law I am dead to the law, [For by the law I am dead to the law, that I live to God;]
20 and I am fixed to the cross, that I live to God with Christ. And now live not I, but Christ liveth in me. But that I live now in flesh, I live in the faith of God’s Son, that loved me, and gave himself for me. [with Christ I am fixed to the cross. Forsooth I live now, not I, but Christ liveth in me. Forsooth that I live now in flesh, I live in the faith of God’s Son, which loved me, and betook himself for me.]
21 I cast not away the grace of God; for if rightwiseness be through law [for if rightwiseness is by the law], then Christ died without cause.”