en_tn/php/03/09.md

be found in him

The phrase "be found" is an idiom that emphasizes the idea of "to be." Alternate translation: "be truly united with Christ" (See: rc://en/ta/man/translate/figs-idiom)

not having a righteousness of my own from the law

Paul knows that he cannot become righteous by obeying the law.

but that which is through faith in Christ

The word "that" refers to righteousness. Paul knows that he can become righteous only by believing in Christ. AT: "but having the righteousness that comes by believing in Christ"