The Catechism in Questions & Answers

582. How did the first Christian congregations come into being?

The first Christian congregation came into being on Pentecost (cf. Acts 2: 37 et seq.). This congregation consisted only of Jews. Owing to the persecutions that followed, many of the believers fled from Jerusalem (cf. Acts 8: 1; 11: 19). In their new surroundings they continued to preach the gospel, which also met with faith there. So it was that Christian congregations began to form in other places.