The Kingdom of God
Mark 9:1 And he said unto them, Verily I say unto you, That there be some of them that stand here, which shall not taste of death, till they have seen the kingdom of God come with power.
Luke 17:20 And when he was demanded of the Pharisees, when the kingdom of God should come, he answered them and said, The kingdom of God cometh not with observation:
Luke 17:21 Neither shall they say, Lo here! or, lo there! for, behold, the kingdom of God is within you.
The kingdom of God is within a redeemed heart, those who trust in Jesus and have been born again of His Spirit. We live not by the flesh but by the Spirit, serving God.
John 3:6 That which is born of the flesh is flesh; and that which is born of the Spirit is spirit.
Mat 12:28 But if I cast out devils by the Spirit of God, then the kingdom of God is come unto you.
Mat 12:29 Or else how can one enter into a strong man's house, and spoil his goods, except he first bind the strong man? and then he will spoil his house.
Mat 12:30 He that is not with me is against me; and he that gathereth not with me scattereth abroad.
Mat 12:31 Wherefore I say unto you, All manner of sin and blasphemy shall be forgiven unto men: but the blasphemy against the Holy Ghost shall not be forgiven unto men.
The Holy Ghost must come to you to witness of Jesus. If we reject the way we come to Jesus, we cannot receive him and be saved from sin and wrath.
Mat 12:32 And whosoever speaketh a word against the Son of man, it shall be forgiven him: but whosoever speaketh against the Holy Ghost, it shall not be forgiven him, neither in this world, neither in the world to come.
Mat 12:33 Either make the tree good, and his fruit good; or else make the tree corrupt, and his fruit corrupt: for the tree is known by his fruit.
If you are just religious after the flesh, your fruit is not good, it is of sin and corruption. If by the Spirit of God, your fruit is good, as the spirit has all good fruit. (Gal; 5:22-23)
His disciples were to get a glimpse of the kingdom of God in the natural world, probably because they only could see with natural eyes, not yet having His Spirit within them.
Mark 9:2 And after six days Jesus taketh with him Peter, and James, and John, and leadeth them up into an high mountain apart by themselves: and he was transfigured before them.
Mark 9:3 And his raiment became shining, exceeding white as snow; so as no fuller on earth can white them.
Peter, James and John were chosen to see the kingdom of God with their natural eyes. Jesus was transfigured, he appeared in his glorified body, shining white as an angel might appear.
Mark 9:4 And there appeared unto them Elias with Moses: and they were talking with Jesus.
The dead were alive! A foretaste of the resurrection. Jesus spoke to Martha, whose brother Lazarus had died:
John 11:25 Jesus said unto her, I am the resurrection, and the life: he that believeth in me, though he were dead, yet shall he live:
John 11:26 And whosoever liveth and believeth in me shall never die. Believest thou this?
John 11:27 She saith unto him, Yea, Lord: I believe that thou art the Christ, the Son of God, which should come into the world.
Elijah and Moses were alive and talking to Jesus.
Mat 22:32 I am the God of Abraham, and the God of Isaac, and the God of Jacob? God is not the God of the dead, but of the living.
Those who believe in the Messiah, Jesus shall live forever. Elijah represented the prophets and Moses the law. Before Jesus came, these were how God spoke to his people. Now God has spoken to us by His Son. Behold the Kingdom of God is come.