Below is a short excerpt concerning how the church relates to the kingdom of God from my book, He Will Reign Forever: A Biblical Theology of the Kingdom of God. Published by Lampion Press (LampionPress.com). This comes from a chapter called “How the Kingdom Relates to the Bible’s Main Characters,” pages 540-42.
The church is an important stage in the kingdom program. The kingdom itself is a broader category than the church and relates to God’s plan to exercise His sovereignty over every aspect of creation—material and immaterial; humans and angels; animals, trees, inanimate objects, etc. The kingdom encompasses other major themes of Scripture including covenants, law, salvation, people of God, etc. The church is a category within the people of God concept. The church is the New Covenant community of believing Jews and Gentiles as it exists in this age between the two comings of Jesus. The church has a worldwide mandate to spread the message of King Jesus in this age while Israel is experiencing a partial and temporary hardening because of unbelief.
The church is not the kingdom, but it relates to the kingdom program in several important ways. First, the church consists of those who have consciously trusted in Jesus the Messiah. The church experiences messianic salvation since its members are joined to the Messiah. By means of the Holy Spirit Jesus baptizes believers into His body, the church. Christ’s church, therefore, comes under the authority of Jesus. Read more about How the Church Relates to God’s Kingdom Program