God did not expect Jews to cease being Jews because they were Christians. This first congregation functioned within its culture . They renounced evil and embraced God's purposes. Paul never asked Christians who were not Jews to adopt Jewish practices. Neither did Paul ask Jewish Christians to cease Jewish practices.
Cultural practices save no one.
Jesus Christ can save anyone. While Paul did not place spiritual confidence in his Jewish heritage, neither did Paul renounce his Jewish heritage. Please note that Paul did not place his confidence in these things. Paul did not renounce Jewish culture, traditions, and practices. Rather, he placed no spiritual confidence in them.