Go rather to the lost sheep of Israel.
6. But go rather to the lost sheep The first rank, as we have said, is assigned to the Jews, because they were the firstborn; or rather, because at that time they alone were acknowledged by God to belong to his family, while others were excluded.
The apostles must not go to the Gentiles or Samaritans because Christ Himself had not revealed Himself to them. The Jews must have first offer of salvation; if they refuse it, Christ hides Himself from that place. This restraint was only for their first mission; afterwards all nations were to receive the gospel.
AI summary
Commenting on Matthew 10:5-15
But go rather to the lost sheep of the house of Israel. To whom he himself was sent, Mat 15:24. By "the house of Israel" is meant the whole Jewish nation; for though this phrase, when distinguished from the house of Judah, designs only the ten tribes; yet here it intends all the Jews, then living in the land of Judea, among whom there were...