Read: Acts 16:1-9
Paul came to Derbe and then to Lystra, where a disciple named Timothy lived, whose mother was Jewish and a believer but whose father was a Greek. The believers at Lystra and Iconium spoke well of him. Paul wanted to take him along on the journey, so he circumcised him because of the Jews who lived in that area, for they all knew that his father was a Greek. Acts 16:1-3
Paul is back at Lystra, the city where he had encountered the most severe opposition of his first missionary journey. There he had led a young man to Christ on that first occasion, who now was still a boy, only about sixteen years old. Paul thought he observed in him various gifts — gifts of ministry, perhaps of wisdom and of knowledge in the Scriptures, of teaching, and of preaching. He wanted to take Timothy with him, using that marvelous means of discipling which has never been superseded, the process and method by which Jesus himself trained men, taking him along with them and teaching him as they ministered together.
But there was a bit of a problem. Timothy was half Jewish, half Greek. His father was a Greek but his mother was a Jew, and, according to the Jews, this made him a Jew. The Jewish people had a very practical way of thinking about this. They said anyone knows who a man’s mother is, but you can’t be as sure of his father. So they reckoned the line of descent through the mother and Timothy was therefore considered a Jew.
The amazing thing is that Paul circumcised Timothy, while earlier he had refused to do the same to Titus. This is not recorded in Acts, but from a parallel passage in Galatians we have learned that he had taken Titus, who was a Greek, with him up to Jerusalem. The Jewish brethren there wanted to circumcise Titus, but Paul absolutely refused. He was adamant because to have permitted it would have been a concession to the idea that you had to become a Jew to become a Christian.