The Law, Paul teaches in the previous few verses, was written against all those who endorse behavior contrary to “the glorious gospel of the blessed God, which he entrusted to” Paul. The fact that God had so entrusted him, or counted him faithful, is the source of the current doxology.
I thank Christ Jesus our Lord, who has given me strength, that he considered me faithful, appointing me to his service. Even though I was once a blasphemer and a persecutor and a violent man, I was shown mercy because I acted in ignorance and unbelief. The grace of our Lord was poured out on me abundantly, along with the faith and love that are in Christ Jesus. Here is a trustworthy saying that deserves full acceptance: Christ Jesus came into the world to save sinners—of whom I am the worst. But for that very reason I was shown mercy so that in me, the worst of sinners, Christ Jesus might display his unlimited patience as an example for those who would believe on him and receive eternal life. Now to the King eternal, immortal, invisible, the only God, be honor and glory for ever and ever. Amen.To put Paul’s “I thank Christ Jesus our Lord, who has given me strength” in bold relief, it must be contrasted with another prayer of thanksgiving offered by a certain man Jesus mentions in the gospels, “God, I thank you that I am not like other men—robbers, evildoers, adulterers—or even like this tax collector. I fast twice a week and give a tenth of all I get” (Luke 18:11–12). Paul’s opponents in Ephesus also had their food laws (4:3) and sought financial gain through their “godliness” (6:5).
What’s the difference? The difference is that “the grace of our Lord was poured out on [Paul] abundantly” (v. 14). Why is it that Christ Jesus came into the world to save sinners as bad as Paul (or as you and I)? It’s because, while unrepentant Pharisees are making lists of who they're better than and all the external requirements they fulfill, Paul is extolling the infinite mercy of Christ to those who believe and the eternal glory of the King who grants them eternal life. Grace to the sinner means glory to the Savior.