It’s the kingdom of God’s message, the gospel Jesus preached. In Matthew Jesus specifically talked about the kingdom of God more than 50 times, more than any other books in the Bible. From Jesus’ declaring on Matt 4:17, the gospel of kingdom of God comes in the following 7 phases: (1) the kingdom of God began from Jesus’ incarnation of God’s word(Matt Ch 1-4), (2) the kingdom of God’s people are to live holy with their rewards(Ch 5-7), (3) the kingdom of God’s preaching is by God’s authority and power(Ch 8-12), (4) the Kingdom of God starts from people’s hearts to churches(Ch13-16), (5) the kingdom of God is to grow in church like in heaven(Ch 17-23), (6) the kingdom of God ‘s coming proceeds with signs to alert His people and its foretold judgments to call others to repent(Ch 24-25), (7) the kingdom of God’s foundation is Jesus’ salvation accomplished on the cross for His people to declare to the world(Ch 26-28). At the end of the Bible, in Revelation Jesus revealed to John more specifics of His kingdom’s coming signs and the glorious hope His people will realize in His final victory to reign with Him, and the judgments for calling the world to turn back to Him. The following youtube shows the Revelation in 16 video briefs.
May God bless you reading and proclaiming His word(Rev 1:3)