Introduction
What was the chief message Jesus taught in his earthly ministry? As Matthew's Gospel introduces the reader to Jesus' public life and ministry, the answer is simple: The Gospel of the Kingdom. This phrase "Gospel of the Kingdom" is understood best when we break it down into its constituent parts. The term "Gospel" means "goodnews". Second, the phrase "of the Kingdom" describes the contents of this goodnews. What follows is a further explanation of the contents and meaning of the idea of "the Kingdom" in the Bible. Three main senses can be identified in explaining the Biblical concept of the Kingdom - with the first two deriving from the Old Testament and the third deriving from Jesus and the New Testament. The first two senses will be brushed over quickly, since the third sense brought out by Jesus dominates the Gospels and the reaminder of the New Testament.
The three senses in which we can understand the Kingdom in the Bible
The term "Kingdom" itself denotes itself in three main senses. First, the "Kingdom" refers to the realm and reign of God over the earth currently and from eternity (Psalm 22:28; 45:6). Second, the kingdom of God is promised to manifest itself fully on the earth (Ezekiel 40-48; 1 Corinthians 15:20-28). These first two senses speak respectively of a "past, eternal, invisible reign of God" and a "future, visible reign of God". This at least summarizes the Old Testament Jewish understanding of God's Kingdom. The third sense of which the Kingdom is spoken of in the Bible is the idea of an "already/not yet" phase of which Jesus introduces in His ministry and which is unfolded more below.
The three senses in which we can understand the Kingdom in the Bible
The term "Kingdom" itself denotes itself in three main senses. First, the "Kingdom" refers to the realm and reign of God over the earth currently and from eternity (Psalm 22:28; 45:6). Second, the kingdom of God is promised to manifest itself fully on the earth (Ezekiel 40-48; 1 Corinthians 15:20-28). These first two senses speak respectively of a "past, eternal, invisible reign of God" and a "future, visible reign of God". This at least summarizes the Old Testament Jewish understanding of God's Kingdom. The third sense of which the Kingdom is spoken of in the Bible is the idea of an "already/not yet" phase of which Jesus introduces in His ministry and which is unfolded more below.
Early Christmas presents illustrate the Gospel of the Kingdom
To hear that the "Kingdom of God" was no longer just something invisible "up there" nor only a reality "yet to come" must had ignited excitement. Since the Kingdom of God is a reality taught in the Bible, a Kingdom necessarily implies a "King". That King, as we have already stated, was no less than God Himself. To hear that the Kingdom was arriving far sooner than expected, and that God Himself may very well be in the midst of the people was jarring - to say the least. This in effect was what Jesus was communicating.
When we speak of the Gospel of the Kingdom, we are referring to what Bible teachers call "an already/not yet" phase. To illustrate, if I told my children I was getting them an early Christmas present, and that the first part of that present was going to be arriving tomorrow, could they truly say they have their Christmas present? In one sense "yes" and in another sense "not yet". Perhaps I give them the batteries or the wheels or whatever the first part may be. Those pieces or parts function as a guarantee and a promise of the remainder yet to come.
A helpful phrase when talking about the Gospel of the Kingdom: "Already, not yet"
Jesus in effect was declaring to His audience that first and foremost, the King had come. He of course being the King, truly God in human flesh (John 1:14). Secondly, the Kingdom of God was in one respect as good as here already. However, the Jews of Jesus' day had to get ready to put on the corrective lenses of the New Covenant teaching of Jesus. They were expecting a fully manifested Kingdom. However, Jesus' point in His Kingdom teaching was "well, not yet, however, follow me by faith, and you'll get a foretaste". Theologian George Eldon Ladd describes the Kingdom of God through the life and ministry of Jesus as "inbreaking" into this present age.
Thinking of the Gospel of the Kingdom as heavenly cake-batter
What would end up occuring would be the Kingdom's chief manifestation occuring in the hearts of believers in this current age. Christians are as it were what I liken to a child eating cake batter. As a child, I can recall my grandmother making cakes. I always hoped she had some left over batter in the bowl. As the cakes baked, I would sit at the table and lick the bowl and cake-beaters clean. I knew full-well that what I was tasting was not "cake" in the strictest sense. However, it was giving me an idea and in another sense, a foretaste of what would be the finished product. I got me excited because I knew that in a few hours, I'd be tasting the fully-finished cake with frosting and all the trimmings. As a child, that was "good-news" indeed. When Jesus proclaimed the Gospel of the Kingdom, He was setting the stage for what would be the central truth of Christianity - namely the King has come, and He will be coming again.