en_tn_lite_do_not_use/phm/01/13.md

in my chains ... while I am in chains

Prisoners were often bound in chains. Paul was in prison when he taught Onesimus and was still in prison when he wrote this letter. Alternate translation: "while I was in prison ... while I am in prison" (See: rc://en/ta/man/translate/figs-metonymy)

so he could serve me for you

"so that, since you cannot be here, he might help me" or "so that he could help me in your place"

for the sake of the gospel

Paul was in prison because he preached the gospel publicly. This can be stated explicitly. Alternate translation: "because I preach the gospel" (See: rc://en/ta/man/translate/figs-explicit)