The kingdom of God

R T France is characteristically helpful as he discusses what the phrase "kingdom of God" (Mark and Luke) or "kingdom of heaven" (Matthew) means:

Rather than denoting a specific time, place or situation called ‘the kingdom’… the phrase ‘the kingdom of God’ in both its Hebrew and Greek forms denotes the dynamic concept of ‘God ruling.’ It represents, in other words, a sentence of which the subject is not ‘kingdom’ but ‘God’. This dynamic sense is now better conveyed by an abstract noun such as ‘kingship’ or ‘sovereignty’ rather than by ‘kingdom’, which has become in general usage a concrete noun. Matthew’s summary of John’s (and Jesus’) declaration, ‘The kingdom of heaven has arrived,’ might thus be paraphrased as ‘God’s promised reign is beginning’ or ‘God is now taking control.’ (Page 102)