Acts 16:3
Him would Paul have to go forth with him; and took and circumcised him because of the Jews which were in those quarters: for they knew all that his father was a Greek. Him would Paul have to go forth with him; and took and circumcised him because of the Jews which were in those quarters: for they knew all that his father was a Greek.
Timothy was the son of a Jewish mother and a Greek father. He had been thoroughly educated in the Jewish religion, and his childhood knowledge of the Scriptures helped prepare him for service. Paul wanted him to go forth with him and chose him as a companion in his work and travels. Timothy was chosen because he was faithful, steadfast, and true, so that his childhood teachers were rewarded when he joined Paul in close fellowship.
In taking Timothy on his journeys, Paul was training a younger worker by giving him experience that prepared him for positions of responsibility, and he continued to support such workers after they were separated. Paul had him circumcised not because God required circumcision, but as a concession to remove an obstacle to preaching Christ among the Jews in those quarters who knew his father was a Greek. Since Paul worked in the synagogues, local Jews would have regarded Timothy as an uncircumcised heathen and rejected his ministry, so the circumcision prevented prejudice from hindering the message.
In doing this Paul sought to bring Jews to Christianity and to avoid giving them a pretext for opposition, accommodating their prejudice only so far as faith allowed. The act did not make circumcision essential or necessary, for circumcision and uncircumcision count for nothing while the gospel of Christ is everything.