It was customary for one who spoke in the synagogue to remain seated (see Luke 4.20). It may have been for the sake of his Gentile readers that Luke said Paul stood up, since in Gentile circles it was customary for a man to stand up when addressing a group. The fact that he motioned with his hand indicates that he was calling for silence and attempting to get the attention of the people.

Gentiles … who worship God is a term used to distinguish these persons from natural-born Israelites. They may have been either full converts to Judaism or Gentiles who sympathized with the Jewish faith and desired to worship the God of the Jews.

Quoted with permission from Newman, Barclay M. and Nida, Eugene A. A Handbook on The Acts of the Apostles. (UBS Handbook Series). New York: UBS, 1972. For this and other handbooks for translators see here .