During the Earthly ministry of Christ this is what Christ told the disciples to do. Simply put, "This was Christ's first commission to Israel". Jesus "forbid" the Kingdom of Heaven message to be preached to the Gentile! Yes. Jesus forbid it!
Matt 10:5-8...These twelve Jesus sent forth, and commanded them, saying, Go not into the way of the Gentiles, and into any city of the Samaritans enter ye not: But go rather to the lost sheep of the house of Israel. And as ye go, preach, saying, The kingdom of heaven is at hand.
Here's a comment from Christ about that "first commission". Jesus said He was directly sent to the House of Israel!
Matt 15:22-27... And, behold, a woman of Canaan came out of the same coasts, and cried unto him, saying, Have mercy on me, O Lord, thou Son of David; my daughter is grievously vexed with a devil. But he answered her not a word. And his disciples came and besought him, saying, Send her away; for she crieth after us. But he answered and said, "I am not sent but unto the lost sheep of the house of Israel".
Mark 7:27...The woman was a Greek, a Syrophenician by nation; and she besought him that he would cast forth the devil out of her daughter. But Jesus said unto her, Let the children first be filled: for it is not meet to take the children's bread, and to cast it unto the dogs.
Gentiles were considered "dogs" in the Old Testament. Even Jesus recognized Gentiles to be "dogs". Jesus also said let the children first be filled making reference to Israel.
John 1:11...He came unto his own, and his own received him not.
John 4:22...for salvation is of the Jews
In order to understand why Jesus forbade the Kingdom of Heaven message to be preached to the Gentiles and Samaritans you have to understand who the Old Testament was written to. You have to understand that Old Testament Promises were given to the Hebrew nation and to the nation of Israel. Gentiles knew nothing about the Levitical Priesthood , the Law of Moses given on Mt. Sinai, or the Prophets of Old who were given all of God's Promises.
The Old Testament contains hundreds of prophecies that pertain to the establishment of God's Kingdom on Earth...but the Gentiles however; knew nothing of these promises or the Holy Scriptures.
The Samaritans had Jewish blood by descent but were set aside by God because they broke their covenant relationship with God as a result of Babylonian religious persuasion. Samaritan's blended pagan religion with Jewish worship of Jehovah...thus they were put out of covenant relationship with Jehovah during the Babylonian captivity.
The Kingdom of Heaven (Heaven on Earth) was promised stictly to the Jew. All Jews knew about the Promise of the Messiah given in Old Testament records. What did Gentiles know about God's Promises given to Israel? Nothing.
Here's the Apostle Paul's description of the Gentiles from the New Testament records.
Eph 2:12...That at that time ye were without Christ, being aliens from the commonwealth of Israel, and strangers from the covenants of promise, having no hope, and without God in the world:
That's the Biblical explanation of why Jesus openly forbade the disciples to take the Kingdom message to the Gentiles.
You may find this teaching to be unusual compared to mainstream teaching but you will find out the truth behind it. Truth takes away confusion! The more you learn about this teaching the more you will learn to rightly divide the Holy Scriptures. May the Lord open the Scriptures to you and bless your future studies!