Jesus is sending them out to teach the message of love for the Supreme Being to a specific group of people. He is also carrying on the teachings of John the Baptist. How do we know this?
Consider these prior verses:
In those days John the Baptist came, preaching in the Desert of Judea and saying, "Repent, for the kingdom of heaven is near." (Matt. 3:2)
From that time on [after Jesus had heard of John's imprisonment] Jesus began to preach, "Repent, for the kingdom of heaven is near." (Matt. 4:17)
And now we find in this verse above that Jesus was telling his own disciples to carry on that same teaching:
"As you go, preach this message: 'The kingdom of heaven is near.’"
These verses indicate that Jesus did not make up his teachings. Once his own teacher - John the Baptist - was imprisoned, Jesus carried on those teachings, and asked his own students to do so as well.
This is the tradition of all the prophets and messengers of God. They each became the student of a teacher, taught those teachings, and then told their students to pass on those teachings.
One might ask why the Gentiles or Samaritans were not to be taught. To answer this we must understand that Jesus is asking his students to teach a particular message to a particular people. It is not as if Jesus’ mercy and teachings are not to be spread to anyone and everyone.
Rather, this is a testament to the fact that particular messages are given at particular times to particular people. For example, a college professor would have an altogether different set of instructions to a college class than a kindergarten teacher would have for a class of kindergartners. The two teachers have the same goal in mind - to teach the children. But their specific information is tailored to the age, maturity and education level of the students.
In the time of Jesus, the Jewish people had access to a collection of knowledge that had been handed down from the great prophets such as Abraham and Moses. As such, teaching specifically to that segment of society had to be altogether different than the teachings Jesus would have for Gentiles and Samaritans. This is not to say that Jesus did not teach to the Gentiles and Samaritans - he certainly did, as evidenced in other verses.
As for the specific instructions he gave them to teach the Jewish people, “The kingdom of heaven is near;” this statement has been blatantly misinterpreted for centuries by politically-oriented, ecclesiastic and sectarian organizations that have sought to create a false sense of urgency among the population. They have been trying to utilize this statement to scare people into coming into their church or sect by teaching that this means the end of the world is coming.
This was begun by the interpretation by the Fourth Century' Council of Nicene - organized by the Roman Emperor Constantine to bring the Christian world under his control. This interpretation has continued as so many sectarian organizations have continued to see fit to scare people into thinking that "the end of the world" is coming so 'we'd best go to church, or we'll go to hell.'
As a result, for many centuries, Christian ecclesiastical teachers have consistently preached that the world is coming to an end based upon this statement by Jesus. (See this page for a partial list.) In each generation, different “signs” have been used together with various quotes of different books within the Bible to offer proof that the world will end next year or even tomorrow.
So many centuries have passed, and still the world has not come to an end. Yet these 'false prophets' are still teaching that the world is coming to an end on a particular date. At what point will we figure out that this interpretation is wrong?
The correct interpretation of "The kingdom of heaven is near" is quite different: The Greek word used is ἐγγίζω, which means, according to the Greek lexicon:
1) to bring near, to join one thing to another
2) to draw or come near to, to approach
Near is not a time element: Near is an element of distance.
More importantly, the Supreme Being in His expansion as the Holy Ghost is right next to each of us: He is truly near.
What does "kingdom" mean?The word "kingdom" is being translated from the Greek word βασιλεία (basileia) - which means, according to the lexicon, "royal power, kingship, dominion, rule" and "not to be confused with an actual kingdom but rather the right or authority to rule over a kingdom." In other words, the word refers to accepting the dominion and power of the Supreme Being. His ultimate authority.
Everything is part of God's kingdom: He owns everything and He controls everything. We can thus have a relationship with Him in whatever part of His kingdom we may reside. The "kingdom" that Jesus is referring to is the consciousness where we are devoted to Him. It is the place in our hearts where we are thinking of Him, and wanting to please Him and do His will.
The kingdom of God is so near that all we have to do is make a decision. We don't have to go anywhere special. We don't have to join any special organization. We don't have to undergo any special ceremony. All we have to do is drop to our knees and ask God directly, by the grace of His representatives like Jesus and Moses, to help us re-establish our loving relationship with Him.
Are we in the kingdom of God now?The physical world is that place where He sends those souls who have rejected Him and have become envious of Him. Each of us living in this physical dimension have decided to reject God at some point. This is the symbolism of Adam's eating of the tree of knowledge in the garden of Eden. Adam (like each of us) rejected God's request not to eat of the fruit. What was that fruit? The fruit is envy - where we wanted to know what it was like to enjoy and be in control like God ("like one of Us, knowing good and evil" Gen. 3:22).
So in this section of God’s kingdom - within the gross physical world - most of us wholly disregard God. We got our wish. We now have the illusion of control - over our physical possessions, our children, our pet, our employees and so on. Yet this is just the illusion of control. We don't really control these people or animals. We just like to think we do.
Indeed, most of us currently seek more control in the form of fame, wealth and a powerful position. We want to be the CEOs, the presidents, the bosses, the judges - and so on. We want to dominate and control others, because we are at heart jealous of the Supreme Being's control.
We are seeking, in fact, the Supreme Being's position. In other words, we are aspiring to gain the position of God. This is the manifestation of our enviousness of God and why we were thrown out of the spiritual dimension (So the LORD God banished him from the Garden of Eden... Gen. 3:23).
Today there are even so-called ‘religious organizations’ that manipulate the teachings of Jesus to proclaim that we are each god. This is the epitome of our envy of the Supreme Being. They are proclaiming that we are all god but we forgot, and now they will teach us to remember we are god.
As if God can forget He is God. This is how far away from God some of us in the physical world have come. We want to enjoy the world as though we were God, and bend His scriptures to accommodate our goal.
So even though we might still be located within the kingdom of God - because everything is within God's kingdom - we are in fact not within His personal kingdom when it comes to our consciousness. We are located outside the personal kingdom of love for God, which is the true kingdom of God.
In the kingdom of love for God, the residents are all concerned about God's happiness. They are concerned about others' happiness. We don't have to imagine such a world, as John Lennon sang. It does exist. We just are not in it because we are self-centered instead of being God-centered.
This is the kingdom that Jesus is referring to as near. This kingdom is ridiculously "near." It is as near as each of us making a decision to change. It is as near as a simple, heartfelt, and apologetic prayer asking forgiveness and offering ourselves to the Supreme Being. It is as near as the ground, where we can place our head and ask the Supreme Being - our Best Friend - if He will take us back, and teach us to love and serve Him again. Jesus illustrated how to do this:
Going a little farther, he fell with his face to the ground and prayed, "My Father, if it is possible, may this cup be taken from me. Yet not as I will, but as You will." (Matt. 26:39)
This simple key opens God’s personal kingdom to us. This is how near His kingdom is.
As for Jesus telling his students to heal the sick, cast out demons, and travel without clothes and money, these are the tools Jesus gave his disciples in order for them to depend upon the Supreme Being and illustrate to others that they can depend upon God.
This is the pure message of Jesus’ instruction: Have complete trust in God and rely upon Him, because He is our Ultimate Savior, and He is near.