Who were the twelve apostles apostles of?
The twelve apostles were apostles of Israel. Jesus commanded them not to go to Gentiles but only to the lost sheep of the house of Israel. Scripture never records a ministry among Gentiles for these twelve men; they were specifically apostles of Israel, as they understood.
Les explains that Jesus chose the twelve and commanded them not to go to a Gentile but only to the lost sheep of the house of Israel (s237-s240). Therefore, the twelve were apostles of Israel (s241-s242). Les notes that you cannot show from Scripture that these twelve men ever had a ministry among Gentiles (s243-s249). While Peter went up to Antioch, an actual ministry among Gentiles is not recorded in the Book (s250-s254). They were the apostles of Israel, and they understood that, though many today do not (s255-s258). Paul later confirms that the Gospel of the uncircumcision was committed to him, just as the Gospel of the circumcision was committed to Peter (s230-s234).