Jesus' Gospel of the Kingdom centred on the call to repentance and the blessings of the Kingdom. His message emphasised the blessings we would receive "in this life" (including forgiveness, having the favour of God and receiving healing) as well as "in the Age to Come, eternal life" (Luke 1829-20). Focal to His message was the Kingdom-ethic: living according to "the golden rule", loving our neighbour (and understanding "neighbour" to mean those who were formerly our enemies), and developing a new sense of justice and fairness based on the standard of grace.
Jesus' Gospel of the Kingdom was not a message that "God is King", but rather in the Kingdom this is how you should live. It was primarily ethical rather than theological. If anything was said about Kingship it was rather that Jesus is King. Matthew's Gospel begins with the declaration that Jesus was "born king of the Jews" (2:2) and Luke's with the angelic announcement that "the Lord God will give him the throne of his father David, and he will reign over the house of Jacob forever; his kingdom will never end" (1:32-33).
Paul uses the Roman Imperial title Lord to declare that a Christian is someone who confesses "Jesus is Lord" (Romans 10:9; 1 Cor 12:3), and says elsewhere that while there is "One God" there is also "One Lord" (1 Cor 8:6; Eph 4:5), Jesus Christ.
Jesus now rules as King. In His own words He said "All authority in heaven and on earth has been given to me" (Matt 28:18). Paul said He is seated at God's "right hand in the heavenly realms, far above all rule and authority, power and dominion, and every title that can be given, not only in the present age but also in the one to come." (Eph 1:20-21) "In Christ all the fullness of the Deity lives in bodily form, and you have been given fullness in Christ, who is the head over every power and authority. " (Col 2:9-10) He has been given this position until "the end", "when he hands over the kingdom to God the Father after he has destroyed all dominion, authority and power" (1 Cor 15:24).
To submit to the authority of Jesus as Lord, as King of the Kingdom of heaven, is honouring to God: "The Father judges no one, but has entrusted all judgment to the Son, that all may honor the Son just as they honor the Father. He who does not honor the Son does not honor the Father, who sent him" (John 5:22-23).