The Jews in Jesus’ time know what the Old Testament prophets have said about the Kingdom of God. Assuming that knowledge, Jesus Christ makes many comments and gives parables showing different aspects of the Kingdom of God.
Only those who respect God and do what he says will be in the Kingdom of God:
28 But what do you think? A man had two sons, and he came to the first, and said, ‘Son, go work today in my vineyard.’ 29 He answered, ‘I will not,’ but afterward he changed his mind, and went. 30 He came to the second, and said the same thing. He answered, ‘I’m going, sir,’ but he didn’t go. 31 Which of the two did the will of his father?”
They said to him, “The first.”
Jesus said to them, “Most certainly I tell you that the tax collectors and the prostitutes are entering into God’s Kingdom before you.
It is difficult for those who trust in riches to be part of the Kingdom of God:
24 The disciples were amazed at his words. But Jesus answered again, “Children, how hard it is for those who trust in riches to enter into God’s Kingdom!
God’s purpose to establish His Kingdom on earth starts insignificantly, and we don’t know how God is working, but it eventually becomes very obvious:
26 He said, “God’s Kingdom is as if a man should cast seed on the earth, 27 and should sleep and rise night and day, and the seed should spring up and grow, though he doesn’t know how. 28 For the earth bears fruit by itself: first the blade, then the ear, then the full grain in the ear. 29 But when the fruit is ripe, immediately he puts in the sickle, because the harvest has come.”
Jesus gives a parable illustrating that the message of God’s coming Kingdom is of more value than anything else:
44 “Again, the Kingdom of Heaven is like treasure hidden in the field, which a man found, and hid. In his joy, he goes and sells all that he has, and buys that field.
The parable of the dragnet teaches that not all who hear the message of the Kingdom of God will have a place in it:
47 “Again, the Kingdom of Heaven is like a dragnet, that was cast into the sea, and gathered some fish of every kind, 48 which, when it was filled, they drew up on the beach. They sat down, and gathered the good into containers, but the bad they threw away. 49 So will it be in the end of the world. The angels will come and separate the wicked from amongst the righteous,
Jesus says that just as young children trust their parents, so we must trust God’s message about the coming Kingdom:
15 Most certainly I tell you, whoever will not receive God’s Kingdom like a little child, he will in no way enter into it.”
Jesus tells his disciples that those who reject the message have had the Kingdom near to them:
10 But into whatever city you enter, and they don’t receive you, go out into its streets and say, 11 ‘Even the dust from your city that clings to us, we wipe off against you. Nevertheless know this, that God’s Kingdom has come near to you.’
After his resurrection, Jesus continues to talk about the coming Kingdom to his disciples:
3 To these he also showed himself alive after he suffered, by many proofs, appearing to them over a period of forty days, and speaking about God’s Kingdom.
The Acts record tells us that the apostle Paul uses the Old Testament to tell his hearers about the Kingdom of God:
23 When they had appointed him a day, many people came to him at his lodging. He explained to them, testifying about God’s Kingdom, and persuading them concerning Jesus, both from the law of Moses and from the prophets, from morning until evening.