The central theme of Jesus' preaching according to the synoptic gospels, and a major subject of scholarly investigation for more than a century.
The term does not occur in the OT; it is mentioned in the book of Wisdom (10: 10) about 50 BCE and in the targum of Isaiah (c. 100 BCE) and was current, though not common, in the time of Jesus. Matthew usually prefers the term ‘Kingdom of Heaven’, which is not to be understood as the realm of the departed hereafter; ‘heaven’ simply reflects Jewish reluctance to utter the divine name.
The primary meaning of ‘kingdom’ is ‘rule’ or ‘sovereignty’ or ‘kingship’, and Jews could not believe that the existing state of the nation, subject to Roman rule, was compatible with the justice of God and the covenant with his chosen people. God their king was bound to intervene. The proclamation of Jesus was that this kingship of God was indeed to break in on the world. Albert Schweitzer wrote the classical exposition of the view that for Jesus the Kingdom lay in the near future. In the Beatitudes, the Kingdom is promised as a future reward. In the Lord's Prayer, the disciples are to pray that the Kingdom will come. Schweitzer maintained that Jesus regarded himself as the Messiah to come and that he went up to Jerusalem to take upon himself the ‘Messianic woes’, the period of suffering sometimes expected by Jews before the coming of the Kingdom, and thus force the hand of God. He was willing to die because God would be obliged to vindicate him. Jesus did not tell the public about his role, and imposed a seal of secrecy on the lips of the disciples, though Judas betrayed this secret to the leaders.
An alternative reading of the synoptic evidence is that Jesus preached that the Kingdom was actually present in his own ministry, as demonstrated by the exorcisms (Luke 11: 20). The main thrust of the parables is that of the mysterious arrival of the Kingdom—e.g. the Hidden Treasure, the Costly Pearl. A greater than Solomon was there! It is these sayings, of the presence of the Kingdom, that make it difficult to accept Schweitzer's theory that Jesus regarded the Kingdom only as God's future intervention. For the Kingdom will not come with apocalyptic signs to be observed but could be discerned already—it is ‘among them’ or ‘within their grasp’ in their own society (Luke 17: 20–21)—if only they would recognize it. The presentness of the Kingdom is obscure and expressed in the parables in which the seed is hidden in the ground or so small that it is almost invisible. Jesus did not encourage expectations that there would soon be a dramatic manifestation of God's rule. He did not foretell an eschatological battle or the intervention of a host of angels, as in the OT book of Daniel, or in the War Scroll at Qumran, or in the Assumption of Moses (a Jewish work probably written during the lifetime of Jesus). Evil, in his view, was to be eliminated by suffering and refusing to retaliate (Matt. 5: 38–48).
The Kingdom is still future in the sense that the Rule of God is not yet fully operative in the world. Like the mustard seed, the rule of God will continue to grow and this is how it will be to the end of time (Mark 4: 26–9). So disciples are to act ‘as if’ they were already members of the Kingdom, ‘as if’ the new Age was already here. Absolute obedience in our human conditions may not be possible, but Jesus by his words and deeds laid down the guidelines which should be our aim, which is to live as though the Rule of God is already in our midst and yet preparing for its ultimate fullness when ethics will be irrelevant.
Modern scholarship has made it plain that in the gospels the Kingdom cannot be identified with the Church, as it has often been since the time of St Augustine, nor can it be envisaged in terms of human virtue or social righteousness, ‘building the Kingdom’. Nevertheless both these interpretations have relevance: the rule of God implies a realm in which rule can be exercised, and the Church is the society which aims to keep alive the incentive and the attraction of the Kingdom. And although the kingdom of God is not to be equated with a human Utopia, there are important ethical and social consequences of embracing or entering the Kingdom, the coming of which is to be sought (Matt. 6: 10). Social hierarchies and class discriminations are irrelevant (Matt. 22: 9–10) and evidently Jesus himself lived out these principles (Luke 7: 33–4). The Rich Young Ruler was asked to give away everything; there must be unquestioning trust in God and selfless love of others; Peter was told to forgive seventy times seven; the Samaritan of the parable did help a wounded Jew. And there could be an allusion to the concept of the Lord enthroned as king in the Holy of Holies in the Temple.