What is the gospel? The word gospel literally means "good news." Christians usually think of the "gospel" as what is found in the books of Matthew, Mark, Luke, and John, which is the written testimonies of the life, death, burial, and resurrection of Jesus, plus His teachings. Jesus used parables (stories) when He taught about the "gospel of the kingdom." He taught that this "kingdom" was still in the future. The righteous would reside there, and He would reign there as their King.
The only place in the Bible that the word "gospel" is defined is in 1st Corinthians 15:1-8, where the Apostle Paul says:
"Moreover, bretheren, I declare to you THE GOSPEL which I preached to you, which also you received and in which you stand, by which also you are saved, if you hold fast that word which I preached to you-- unless you believed in vain. For I delivered to you first of all that which I also received: that CHRIST DIED FOR OUR SINS ACCORDING TO THE SCRIPTURES, AND THAT HE WAS BURIED, AND THAT HE ROSE AGAIN THE THIRD DAY ACCORDING TO THE SCRIPTURES, AND THAT HE WAS SEEN BY CEPHAS, THEN BY THE TWELVE. AFTER THAT HE WAS SEEN BY OVER FIVE HUNDRED BRETHREN AT ONCE, OF WHOM THE GREATER PART REMAIN TO THE PRESENT, BUT SOME HAVE FALLEN ASLEEP. AFTER THAT HE WAS SEEN BY JAMES, THEN BY ALL THE APOSTLES. THEN LAST OF ALL HE WAS SEEN BY ME ALSO, AS BY ONE BORN OUT OF DUE TIME."