The Gospel preached by Jesus Christ when upon the earth had reference to the Kingdom of God.1

Now after that John was put in prison, Jesus came into Galilee, preaching the gospel of the kingdom of God (Mark 1:14).

And Jesus went about all Galilee, teaching in their synagogues, and preaching the gospel of the kingdom (Matthew 4:17, 23).

And he said unto them, I must preach the kingdom of God to other cities also: for therefore am I sent. (Luke 4:43).

And it came to pass afterward, that he went throughout every city and village, preaching and shewing the glad tidings of the kingdom of God: and the twelve were with him (Luke 8:1).

Additional Testimonies (Matthew 9:35; 6:33; 13:19; Luke 9:11; 13:28)

1 In several instances, the form of this proclamation is in the words, The kingdom of God is at hand," or to be critically correct, "has approached." We never find that the apostles made use of this form of proclamation after Christ's ascension. In what sense had the kingdom come nigh, or approached when Christ appeared? In two senses. He brought near the kingdom for offer as an inheritance. The kingdom had never before been preached. "The law and the prophets were until John: since that time the kingdom of God is preached "(Luke 16:16). Secondly, Jesus himself was the kingdom in the germ - see Mark 11:10: "Blessed be the kingdom of our father David, that cometh in the name of the Lord." The original word basileia, translated kingdom, has this comprehensive significance in its secondary sense: royal power, majesty, kingly dignity. Jesus, the manifestation of God's power, which was afterwards to bloom into a universal political administration, was among the people, had approached, and brought the offer of the kingdom with him.