Paul is emphasizing through litotes that God worked through Paul. Alternate translation: "because he was kind to me, I was able to do much good work" (See: [[rc://en/ta/man/translate/figs-litotes]])
Paul speaks of the work he was able to do because God was kind to him as if that grace were actually doing the work. Alternate translation: Possible meanings are 1) this is literally true, and God actually did the work and kindly used Paul as a tool or 2) Paul is using a metaphor and saying that God was kind to let Paul do the work and to make Paul's work have good results. (See: [[rc://en/ta/man/translate/figs-metaphor]])