Why couldn't the apostles minister to the Gentiles at this time?
The apostles could not yet minister to the Gentiles because Israel first had to recognize that the crucified One was their Messiah and He could have returned to set up the Kingdom. Their role required them to remain in Jerusalem awaiting the King, so they stayed there despite persecution.
Les explains that the Twelve knew their role and knew they could not have a ministry to the Gentiles until Israel had come to recognize that the One they crucified was their Messiah, and He could have come and set up their Kingdom. Using an airport or train station analogy, he says they did not want to leave Jerusalem because if the King returned while they were away in Alexandria, Greece, or Italy, they would miss Him. So they sat tight in Jerusalem seven years after Pentecost, even under the persecution Saul of Tarsus brought. The scattering in Acts 11:19 follows the earlier dispersal noted in Acts 8:1.