Some think the Church is the Kingdom of God. Although there is a connection between the two, they are not identical. Jesus Christ is the Head of the Church (Ephesians 1:22 Ephesians 1:22And has put all things under his feet, and gave him to be the head over all things to the church,
American King James Version×), which is the body of believers called by God to proclaim the coming Kingdom.
Christ rules His Church, thus it is under His sovereignty and royal power. We might say the Church is the precursor of the coming Kingdom of God. Or, to put it in terms that Jesus Christ used, we can say that the Kingdom of God is similar to the proverbial mustard seed, waiting for its germination and rapid growth at Jesus' return (Matthew 13:31-32 Matthew 13:31-32  Another parable put he forth to them, saying, The kingdom of heaven is like to a grain of mustard seed, which a man took, and sowed in his field:
 Which indeed is the least of all seeds: but when it is grown, it is the greatest among herbs, and becomes a tree, so that the birds of the air come and lodge in the branches thereof.
American King James Version×).
The Bible, however, never uses the term "kingdom" to apply directly to the Church. Instead, it refers to God's prophesied world-ruling government.