Matthew 10:5 These twelve Jesus sent out and commanded them, saying: “Do not go into the way of the Gentiles, and do not enter a city of the Samaritans.
6 But go rather to the lost sheep of the house of Israel.
Jesus sends out the 12 with orders. Your mission is to go throughout Israel. Proclaiming the kingdom of God is at hand. The Lord would later reach out to Samaria and the outer regions of the gentiles, but now was the time for Israel to recognize their messiah. The holy scriptures came thru the Jewish nation. The "do nots" are as important as the do's." Besides, I dont think these 12 were ready theologically for the gentiles. Reach out first to those close to you, whom you know. Who know you. The early church learned this as they first started in Jerusalem, Judea, then Samaria, then the ends of the earth.