Question: Why did Jesus tell his disciples not to go to the Samaritans or the gentiles, but only the children of Israel to help them? This is in Matthew 10:5.
Answer: That's a great question, because we understand that Jesus' offer of salvation is extended to everyone (John 3:16), and if that's the case, why would he tell his workers, “...Go nowhere among the Gentiles and enter no town of the Samaritans..." ?
We find the direct answer a little further in Matthew at 15:24. “...I was sent only to the lost sheep of the house of Israel.” Since the Father sent Jesus only to the Jews, logic excluded everyone else as a target. Jesus was not being mean by singling out groups to exclude. He was merely giving the disciples the information they needed to perform his Father’s will at that moment. But since that direct answer is probably less than satisfying, let's look at the full answer which plays out across the remainder of Matthew.
There are only two categories of people today: Christians and non-Christians. But in Jesus’ time there were two different categories of people: Jews and Gentiles. No one could become a Christian then, because there was no such thing to become! But something changed after Matthew 10:5 that made Jesus change his marching orders from “Go nowhere among the Gentiles” to “Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all that I have commanded you...” (Matthew 28:19–20, ESV).
So, if your original question contained the underlying, “Why did you shun these people forever, Jesus?” the answer is that he did not. Eighteen chapters later, he included all nations in the commission. But if your question is more toward, “What’s going on? Why the initial restrictions? Why the change?” then consider the following.
When Jesus took on human form, he also took on our common restrictions. Like us, Jesus worked his administrations one after the next, moment following moment, day following day. We must, therefore, always consider the point in time of any occurrences, because God deals with humanity in real time, and he often reveals more of his will at points throughout time. At the time of Matthew 10:5, Jesus had not yet completed his corporal testimony to the Jews, placing this verse before God’s next big revelation. The official work of reaching the nations would soon be assigned to a new (and until then an unknown) entity, the Church, the Body of Christ. But this entity could not appear until after Jesus’ resurrection and after his return to heaven. (John 14) So, your verse places Jesus at a point on a timeline where God continued to give the Jews every opportunity to grab his flag and run—but right before they officially blew it. After Jesus’ final trip into Jerusalem, the Jews simply ran out of time.
If the Jews had acted on Jesus’ messiahship, then they would have remained the standard-bearers for God…but the redemption story would have been much different. We know that Jesus had to die to atone for our sin—there was no other way. But if the Jew's received him officially, who would have done the killing? I'm not sure. The fact is that he died at the hands of his own people. We needed that sacrifice. But did Jesus really need that insult? Actually...he did. Such was the price of our souls.
In summary, all God’s dealings with people occur on a time line, and Matthew 10:5 landed on a point in time before God redefined mankind and reassigned his duties. Therefore we must consider Jesus’ initial restrictive utterance as a necessary part of the greatest story ever told, and when telling it, we must always consider its conclusion: "Go therefore and make disciples of all the nations…”