ISB ~ Acts 16 v3

circumcised:Paul thought it advantageous to circumcise Timothy so their joint ministry among the Jews would not be hindered by scandal (1 Cor 9:20). At this stage, circumcision and other ritual observances of the Torah were permitted for Jewish believers even though unnecessary for Gentiles (15:111). Timothy’s descent from a Jewish mother seems to put him in the former category. Later rabbinic law states that religious affiliation followed matrilineal lines, so that children born of a Jewish mother were automatically Jewish, regardless of the faith of the father.