Adam Clarke on Acts 13:43

Many of the Jews - Direct descendants from some of the twelve tribes; and religious proselytes, heathens who had been converted to Judaism, and, having submitted to circumcision, had become proselytes of the covenant: though some think that the expression means proselytes of the gate - persons who believed in one God, like the Jews, but who had not received circumcision.

Persuaded them to continue in the grace of God - That is, that they should continue to credit the Gospel; to receive the spirit and influence of it; to bring forth the fruits of that spirit; and thus continue under the favor and approbation of God.