The Jews of Jesus’ time generally assumed that they would automatically be citizens of the promised Kingdom (just as being born of British parents living in the United Kingdom automatically makes us citizens of that kingdom). The preaching of both John the Baptist (Matthew 3:2,9) and Jesus (Luke 13:28-30) hit hard at this complacency. It would be possible for true-blooded Jews to be shut out of the Kingdom – and for Gentiles to be welcomed in!
So who is in the Kingdom of God? Jesus has told us: it is, firstly, a kingdom of righteousness (Matthew 13:43). As we have already seen, it will not be sufficient to be born a Jew; but it will also not be sufficient to have a purely nominal membership of the Christian church (Matthew 7:21)! There will be no room for any kind of sin or wickedness (Galatians 5:19-21; Ephesians 5:5). No ‘major’ sins (like sexual immorality, idolatry, or witchcraft) – but also none of the sins that we would consider more ‘everyday’ (jealousy, ambition, drunkenness, greed…) “Those who live like this will not inherit the Kingdom of God.” (Galatians 5:21) And it is impossible for us to take any material wealth into it (Mark 10:23-25). These criteria would seem to exclude just about everybody (Mark 10:26). Those who are privileged to be in the kingdom will be more righteous than even the scribes and Pharisees (Matthew 5:20)!
But Jesus also said some other things about the Kingdom. It belongs to “the poor in spirit” (Matthew 5:3), to those who are “like a little child” (Mark 10:15), and to “those who are persecuted because of righteousness” (Matthew 5:10). When Jesus preached about the kingdom of God He brought “good news” (Mark 1:14,15) – because He declared that anyone (not just the rich, or those with the ‘correct’ background, or those with the self-discipline to keep all the regulations of the Law) could enter the Kingdom! We can’t earn our place in the kingdom, but we can receive it as a gift from God – by acknowledging our sinfulness, casting ourselves upon His mercy, and accepting the cleansing of His Holy Spirit (John 3:3,5). “The wicked will not inherit the Kingdom of God… and that is what some of you were. But you were washed, you were sanctified, you were justified in the name of the Lord Jesus Christ and by the Spirit of our God.” (I Corinthians 6:9-11)