First is 2 Peter written by Peter? Second what did Paul do in the temple? What was the ritual Nazarite vow for? Why would Paul, knowing that the Mosaic regime was obsolete, submit to a “purification” ritual?
Paul already answered that... You know he did but you pretend you don't. He became a Jew to the Jews so that he would draw them to salvation. If the lack of circumcision was to be a stumbling block for their salvation, then circumcision it would be!