The Kingdom of God is a moral kingdom that God has in this world, where His authority is recognized and His character is reflected. We are not told of it’s beginning, although it is never spoken of as being present until Jesus was here on earth. When Jesus was here, He was the embodiment of the kingdom (Luke 17:20-21). The Kingdom of God will never end, because in the eternal state all things are according to God’s mind and suited to His moral character.
A moral kingdom. Romans 14:17 tells us that the kingdom of God does not consist of physical things, but of moral qualities that reflect the character of God. “For the kingdom of God is not meat and drink; but righteousness, and peace, and joy in the Holy Ghost.”
Compared to the Kingdom of Heaven. The kingdom of God is a broad term found in all four gospels and some of the epistles, while the kingdom of heaven is a specific dispensational term only found in Matthew’s gospel. It is one aspect or facet of the kingdom of God. The “kingdom of heaven” refers that state of things where the heavens rule now that Jesus is cast out from the earth. The kingdom of heaven did not “come” until Christ returned to the Father. But the kingdom of God was already “come” unto them (Matt. 12:28) in the Person of the King. Therefore, when you get the kingdom of heaven you also have the kingdom of God there, but certain things are said of the kingdom of God that could not be said of the kingdom of heaven. It is important to distinguish the kingdom of heaven from the kingdom of God because Christ must have a literal kingdom in this earth, and in no way does a moral conformity to God’s character replace that promised kingdom!