The Zondervan Pictorial Encyclopedia of the Bible says this about the Kingdom of God: "The word 'kingdom' is found fifty-five times in Matthew; twenty times in Mark, forty-six times in Luke and five times in John. When allowance is made for the use of the word to refer to secular kingdoms and for parallel verses of the same sayings of Jesus, the phrase 'the Kingdom of God' and equivalent expressions (e.g., 'Kingdom of heaven,' 'his kingdom') occur about eighty times . . . These statistics show the great importance of the concept in the teachings of Jesus . . . There can, therefore, be little doubt that the phrase 'the Kingdom of God' expresses the main theme of His teaching" (Vol. III, Zondervan, 1976, p. 804).
Jesus equated receiving salvation with entering the Kingdom (Matthew 19:16-24 Matthew 19:16-24  And, behold, one came and said to him, Good Master, what good thing shall I do, that I may have eternal life?
 And he said to him, Why call you me good? there is none good but one, that is, God: but if you will enter into life, keep the commandments.
 He said to him, Which? Jesus said, You shall do no murder, You shall not commit adultery, You shall not steal, You shall not bear false witness,
 Honor your father and your mother: and, You shall love your neighbor as yourself.
 The young man said to him, All these things have I kept from my youth up: what lack I yet?
 Jesus said to him, If you will be perfect, go and sell that you have, and give to the poor, and you shall have treasure in heaven: and come and follow me.
 But when the young man heard that saying, he went away sorrowful: for he had great possessions.
 Then said Jesus to his disciples, Truly I say to you, That a rich man shall hardly enter into the kingdom of heaven.
 And again I say to you, It is easier for a camel to go through the eye of a needle, than for a rich man to enter into the kingdom of God.
American King James Version×), and He explained the loss of salvation in terms of banishment from the Kingdom (Luke 13:28 Luke 13:28There shall be weeping and gnashing of teeth, when you shall see Abraham, and Isaac, and Jacob, and all the prophets, in the kingdom of God, and you yourselves thrust out.
American King James Version×). The message of salvation is called "the word of the kingdom" (Matthew 13:19 Matthew 13:19When any one hears the word of the kingdom, and understands it not, then comes the wicked one, and catches away that which was sown in his heart. This is he which received seed by the way side.
American King James Version×). The hope and comfort of a Christian are said to be in entering the Kingdom (Mark 10:15 Mark 10:15Truly I say to you, Whoever shall not receive the kingdom of God as a little child, he shall not enter therein.
American King James Version×).
The goal of a Christian is to "seek first the kingdom of God" (Matthew 6:33 Matthew 6:33But seek you first the kingdom of God, and his righteousness; and all these things shall be added to you.
American King James Version×). Righteous people are called "sons of the kingdom" (Matthew 13:38 Matthew 13:38The field is the world; the good seed are the children of the kingdom; but the tares are the children of the wicked one;
American King James Version×). The theme of many of Christ's parables is God's Kingdom (Matthew 13:44-47 Matthew 13:44-47  Again, the kingdom of heaven is like to treasure hid in a field; the which when a man has found, he hides, and for joy thereof goes and sells all that he has, and buys that field.  Again, the kingdom of heaven is like to a merchant man, seeking goodly pearls:  Who, when he had found one pearl of great price, went and sold all that he had, and bought it.  Again, the kingdom of heaven is like to a net, that was cast into the sea, and gathered of every kind:
American King James Version×).
Some of the many biblical terms for and references to the Kingdom of God are explained in our free booklet The Gospel of the Kingdom.