The Gospel of the Kingdom in Romans
It might seem strange that in the letter which has been described as “the Gospel according to Paul” – the letter to the Romans – there is no mention at all of the kingdom. Did Paul change his message? This is hardly possible, especially since we read in Acts that while in Rome he “boldly and without hindrance preached the kingdom of God and taught about the Lord Jesus Christ.” (Acts 28:31). We get a very specific statement from Paul himself about this. While speaking to the elders of the church in Ephesus he said that “the ministry which I received from the Lord Jesus” was “to testify to the gospel of the grace of God”. And then in the next verse he says "I have gone preaching the kingdom of God” (Acts 20:24-25). So to Paul “the gospel of grace” was the same as the gospel of the kingdom. In Romans he teaches about grace, using the word at least twenty times, although never using the word “kingdom”.
The message here is clear: the Kingdom of God is a gift. We cannot earn it. We do not work for it. It is not a reward for services rendered. It is a gift. It is so important that we understand this that Paul writes his “Gospel” – the letter to the Romans – to spell this out clearly.
The Gospel of the Kingdom in Hebrews
The writer to the Hebrews says “since we are receiving a kingdom that cannot be shaken, let us be thankful, and so worship God acceptably with reverence and awe” (Heb 12:28). Elsewhere in his letter he refers to “the city of God” (11:10, 16; 12:22), “the city that is to come” (13:14), “the heavenly Jerusalem” (12:22) and our “homeland” (11:14). The letter emphasizes that we are on a pilgrimage toward this kingdom, or homeland. While the references are predominantly future he does say “you have come to Mount Zion, to the heavenly Jerusalem, the city of the living God” (12:22) in the context of saying that we have come to God and to Jesus (vv. 23-24). So while our hope of the kingdom is future, there is also a sense in which it is also “now”.
The writer to the Hebrews also refers to "the age to come" in an interesting "now, but not yet" way. “For it is impossible for those who were once enlightened, and have tasted the heavenly gift, and have become partakers of the Holy Spirit, and have tasted the good word of God and the powers of the age to come, if they fall away, to renew them again to repentance” (Hebrews 6:4-6). The "now" kingdom reality is a "taste" of the "not yet" final consummation in the age to come. The writer again emphasises that the kingdom is a heavenly gift, highlighting again that the Gospel of the kingdom is the Gospel of grace.