As Christians, we must understand what the Kingdom of God is truly about. Popular Christianity has separated the teachings of Jesus from its gospel preaching, drastically weakening the Gospel! Jesus taught about the Kingdom as the top priority: "But seek first God’s Kingdom and His righteousness ... " (Matt. 6:33). If we desire to understand the truth about the Kingdom, then we must be sure that our definition aligns with the original understanding of the Kingdom, when the promise of the Kingdom to Abraham (Rom. 4:23), to Jesus and to us was made. We must go back to the original covenant with Abraham to grasp the understanding of our future and the future of the world. After all, God created the world and everything in it, including man, and He said that it was good. When sin and refusal to obey God entered the world, it became a sin-cursed world. God wants to restore it to paradise, the condition it enjoyed originally when it was good. Isaiah 49:8 tells us that God wants to restore the land: "This is what YAHWEH says: ‘In the time of my favor I will answer you, and in the day of salvation I will help you; I will keep you and will make you to be a covenant for the people, to restore the land.’"
God made His first covenant concerning the land with Abraham. God called Abraham out of the land of Ur to the land of Canaan and promised the land to him in Genesis 13:14-15: "YAHWEH said to Abram after Lot had parted from him, ‘Lift up your eyes from where you are and look north and south, east and west. All the land that you see I will give to you and your offspring forever.’" This is well-known to scholars: "A constant feature in the eschatological [about the future] picture of the Old Testament is Israel’s restoration to its own land...The question how in our day we are to interpret such prophecies is a double one. It is a question, first, of what the prophets meant. And to this question there can be but one answer - their meaning is the literal sense of their words. They ... predicted the restoration of the people to their land...There is no question as to the meaning of the Old Testament prophecies." 
This is a promise that clearly has not been fulfilled yet: "The whole land of Canaan, where you are now an alien, I will give as an everlasting possession to you and your descendants after you; and I will be their God" (Gen. 17:8). Under Joshua, they did have possession of most of the land, but not all of it (Joshua 15:63; 16:10; 17:12-13). But they did not have it forever! The promise to Abraham concerned an everlasting possession, yet we know that in the book of Judges, God’s people gave in to worshiping idols (which contradicts the promise in Gen. 17:8 that the one God will be their God), and they were conquered on multiple occasions. That leaves us with two options. Either God is a liar and Abraham and his descendants won’t possess the land forever, or this event is still coming in the future after our resurrection to immortality (1 Cor. 15:23).
The truth then is that the promise of gaining the land forever is for us and for the faithful of all times, including Abraham, who will be resurrected to life from their present sleep of death (Ps. 13:3).
This covenant continued through the line of Isaac and Jacob and on through David. Then the same covenant was reestablished with more detail. God says to David, "I will raise up your offspring to succeed you, who will come from your own body, and I will establish his kingdom. He is the one who will build a house for my Name, and I will establish the throne of his kingdom forever. I will be his father, and he will be my son" (2 Sam. 7:12-14). This promise was fulfilled (only partially however, so far) through Jesus, the Messiah. Hebrews 1:5 refers the promise to Jesus.
If we are truly to understand what the Gospel is today, we must define it accurately to match with Scripture. Our culture has defined the gospel, and reduced its scope dramatically, to be only about Jesus’ death and resurrection. If we take an honest look at Scripture, we will notice a very different picture. In Luke 9:6, we find that the Apostles went from village to village, preaching the Gospel. Chronologically, however, after this event, we read that they didn’t even yet understand or believe that Jesus, their Messiah, would die and rise again: "‘He will be handed over to the Gentiles. They will mock him, insult him, spit on him, flog him and kill him. On the third day he will rise again.’ The disciples did not understand any of this. Its meaning was hidden from them, and they did not know what he was talking about" (Luke 18:32-34).
Here is the critical point to grasp and teach: If the gospel was only about Jesus’ death and resurrection, they couldn’t have been preaching it! They didn’t at that stage know anything about it. But they had been learning and preaching the Gospel of the Kingdom as they heard if from Jesus. The good news is truly firstly about the Kingdom. Look at what Jesus had to say as to the reason for his whole ministry: "But he said, ‘I must preach the Gospel of the Kingdom of God to the other towns also, because that is why I was sent" (Luke 4:43). Jesus certainly believed that the good news, Gospel, was about the Kingdom. Look again at what Jesus proclaimed as the saving good news: "After John was put in prison, Jesus went into Galilee, proclaiming the good news of God. ‘The time has come,’ he said. ‘The kingdom of God is near. Repent and believe the good news’" (Mark 1:14- 15). Although the Gospel didn’t yet include Jesus’ death and resurrection, it was still the Gospel. We must not, of course, diminish the vital importance of Jesus’ sacrifice and resurrection.
It was after Jesus’ ascension that we notice an addition to the Gospel message. Certainly, the apostles were now proclaiming the resurrection of Jesus. However, they did not for a moment forget about the Kingdom. But today, where is the Kingdom in the Gospel? It has disappeared.
In Acts, we see key texts showing us clearly what the Apostles were proclaiming: "But when they believed Philip as he preached the good news [Gospel] about the Kingdom of God and the name of Jesus Christ, they were getting baptized, both men and women" (Acts 8:12). "From morning till evening [Paul] explained and declared to them the Kingdom of God and tried to convince them about Jesus from the law of Moses and from the Prophets" (Acts 28:23). Lastly, "Boldly and without hindrance [Paul] preached the Kingdom of God and taught about the Lord Jesus Christ" (Acts 28:31). Clearly, as the apostles taught it, obeying Jesus, the Gospel message included the Kingdom of God (which is near, "at hand") and the fact that Jesus was truly the Messiah who had been prophesied (Deut. 18:15-18).
In the first chapter of Acts, after Jesus’ death and resurrection, we read that he appeared to them over a period of forty days and instructed them about the Kingdom of God (Acts 1:3). He could have spent that time talking about his resurrection or our future resurrection or even baptism, but he didn’t. Of utmost importance, after proving he was the Messiah raised by God from the dead ("for you will not let your holy one see decay" [Acts 2.27, Ps. 16.10]), was the coming Kingdom. The Jews who didn’t believe that Jesus was the Christ, although they believed in the prophesied Messiah, thought that the Messiah ought to have brought in the Kingdom at his first coming.
I can only imagine how much the disciples learned in the precious time they spent with Jesus during those forty days. Six weeks is a very long time for a seminar! But it takes that sort of time to teach people the Bible. Are you dedicating that sort of instruction and learning time to the Gospel so that you may bring the Good News about immortality to your friends? We are commissioned to bring the same Gospel to others in our time. That is the great Commission commanded by Jesus (Matt. 28:19- 20). How well are you doing the will of God and of Jesus in this respect?
In Matthew 13 alone, there are about seven parables. Every single one of them is concerned with the Kingdom of God. The fact that Jesus used seven different illustrations to explain the Kingdom of God tells me that this is a very large, in-depth and important doctrine that we must thoroughly digest and pass on. We even see from the parable of the sower that the teaching of the Kingdom is so important that whenever someone hears it and doesn’t understand it, the evil one, the Devil, comes and tries to snatch it away. If this was a minor teaching, Satan might not even care if it is snatched away! But the Devil knows, better than many churchgoers, that the Gospel/word of the Kingdom (Matt. 13:19) is the fundamental issue in salvation and believing and obeying Jesus. The person who hears about the Kingdom and understands it, the seed that fell on good soil, produces abundant fruit. That is to be our ambition also.
In Luke 22:29-30, Jesus tells the apostles: "I covenant to you a Kingdom, just as my Father covenanted it to me, so that you may eat and drink at my table in my Kingdom and sit on thrones, administering the twelve tribes of Israel." Luke earlier tells us that the people thought that the Kingdom of God was going to appear at once because Jesus the king was near the capital of the Kingdom! [i.e. Jerusalem - Luke 19.11ff] So he taught the parable of the ten minas. Jesus was the man of "noble birth" who went away to a distant country to be appointed king (Psalm 110:1: "YAHWEH said to my lord, ‘Sit at my right hand until I make your enemies your footstool’"). After he is appointed as king (clearly by God, Acts 2:36: "Therefore let all Israel be assured of this: God has made this Jesus, whom you crucified, both Lord and Christ"), he will then return. Just as in the parable, the servants are given responsibilities in life (Deut. 30:19: "I have set before you life and death...Now choose life, so that you and your children may live."). The servants in the parable are given talents to be put to use in the service of the Gospel. The first servant was responsible and his mina earned ten more. This pleased the king! So the king told him, "Take charge of ten cities." So with the second servant. The third servant however squandered the gift and was barred from the Kingdom.
We are commanded multiple times in the Bible to "keep God’s commands." Therefore we would be wise to keep Revelation 2:25 in mind: "Hold fast what you have until I come." One day Jesus will return and we need to be ready for it and busy with Kingdom/Gospel work. Matthew 24:44 warns us to be on the alert because we do not know at what hour the Son of Man will return. He might even come at a time when we do not expect him.
The simplicity and importance of Psalm 110:1 cannot be overstated. Jesus will remain at the right hand of the Father until God makes Jesus’ enemies his footstool. Acts 3:21 tells us the same thing: "He must remain in heaven until the time comes for God to restore everything, as he promised long ago through his holy prophets."
Here is more on the Christian destiny and hope: In Revelation 2:26, "To him who overcomes and does my will to the end, I will give authority over the nations" and 3:21, "To him who overcomes, I will give the right to sit with me on my throne, just as I overcame and sat down with my Father on his throne." The Apostles knew very well what their role would be in the Kingdom.
Against some popular ideas today, Jesus did not teach anything that contradicts the law. But he did not repeat the law in the letter! He fulfilled it, giving it all its ultimate meaning. In fact, Jesus said in Matthew 5:17-19, "Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them. I tell you the truth, until heaven and earth disappear, not the smallest letter, not the least stroke of a pen will by any means disappear from the Law until everything is accomplished. Anyone who breaks one of the least of these commandments and teaches others to do the same will be called least in the kingdom of heaven, but whoever practices and teaches these commands will be called great in the kingdom of heaven." It is imperative that Christians see the correlation between what the prophets said and what Jesus did and what is still to come. It is a part of one symphony that has only been partly accomplished.
As John Bright rightly explains, "For the concept of the Kingdom of God involves, in a real sense, the total message of the Bible. Not only does it loom large in the teaching of Jesus, it is to be found, in one form or another, through the length and breadth of the Bible ... Old Testament and New Testament thus stand together as the two acts of a single drama. Act I points to its conclusion in Act II, and without it the play is an incomplete, unsatisfying thing. But Act II must be read in the light of Act I, else its meaning will be missed. For the play is organically one. The Bible is one book. Had we to give that book a title, we might with justice call it
‘The Book of the Coming Kingdom of God.’" 
It is important to know where we have come from. The root of the Gospel is the promises made to Abraham, the work of King Messiah Jesus, and the future reward for submission and obedience.
 "Eschatology," Hastings Dictionary of the Bible, New York: Charles Scribner’s Sons, 1911, vol. 1, p. 737.
 The Kingdom of God, New York: Abingdon Press, 1953, pp. 7, 197.
Taken from: http://www.focusonthekingdom.org/148.pdf