These twelve Jesus sent out with the following instructions: "Do not go among the Gentiles or enter any town of the Samaritans. Go rather to the lost sheep of Israel. As you go, proclaim this message: 'The kingdom of heaven has come near.' Heal the sick, raise the dead, cleanse those who have leprosy, drive out demons, Freely you have received, freely give." Matt. 10:5-8, NIV.
The first four verses of Matthew 10 list the names of the 12 disciples, whom Jesus now calls "apostles." Here we have a shift in terminology that points to a change in the role of the twelve. Up to then they had been "disciples," learners or followers. But now Jesus identifies them as "apostles," from the Greek apostolos, meaning "one sent as a messenger."
Prior to this time the twelve have been like passengers in a car. Now Jesus is handing them the keys. And just as riders often don't pay much attention to exactly how things are done in varying circumstances--when to make this turn and that--and thus need a bit of careful instruction by their parents before they set out on their maiden voyage, so it is that Jesus has some very definite counsel on how the twelve should carry out their mission.
First, He counsels, stick with Jewish audiences. Don't even attempt to go to the Samaritans or Gentiles.
That sounds like a strange command from a Man who came as Savior of the whole world. But Jesus had His reasons. For one thing, the disciples weren't ready mentally to deal with the Gentiles. Even years later, Peter in Acts 10 would find it almost impossible to enter the house of a Gentile until God gave him a revelation that it was all right. And afterwards he still had to repeatedly defend his actions.
A more important reason for not going to the Gentiles was because of Jewish prejudice itself. If Jesus' followers had aggressively begun working among the Gentiles, no self-respecting Jew would have paid them any attention. It would have confirmed Jesus' enemies suspicions that He was in league with the devil.
The widening of mission will come, and demonstrated by the book of Acts. But meanwhile, Jesus has provided us with an important evangelistic hint. Namely, always start by putting your first energies into that which is close at hand rather than indulging in useless dreams about future "glory" in some far-off land.