Matthew 10:5,6

These twelve Jesus sent forth Namely, to preach the gospel and to work miracles; exercising therein his supreme authority over his Church. And commanded, Go not into the way of the Gentiles That is, into their country. Their commission was thus confined now, because the calling of the Gentiles was deferred till after the more plentiful effusion of the Holy Ghost on the day of pentecost. And into any city of the Samaritans enter ye not In travelling through Palestine the apostles would often have occasion to go into Samaria; but they were not to enter the cities thereof with a design to preach. It is true, in the beginning of his ministry, our Lord himself preached to the Samaritans with great success, John 4:41; and therefore, had he sent his apostles among them, numbers, in all probability, would have been induced to believe; but the inveterate enmity which the Jews bore to the Samaritans made the conversion of the latter improper at this time, as it would have laid a great stumbling-block in the way of the conversion of the Jews: as preaching now to the Gentiles would also have done. But go rather to the lost sheep of the house of Israel He calls the Jews lost sheep, because, as he had told his disciples, Matthew 9:36, they fainted, and were scattered abroad, as sheep having no shepherd, and so were in danger of perishing. See Isaiah 49.