Honestly, I can't believe I need to write and entire blog post to explain this one, but apparently there are Christians who really do believe that Jesus taught one Gospel and that Paul taught another.
[Hint: they did no such thing]
So, in the interest of debunking this nonsense, let me explain a few things:
What's the Gospel of the Kingdom, you ask? Well, very simply, it's the "Good News" that the Kingdom of God where He rules and reigns can be experienced today by anyone who surrenders their life to Christ as their King and begins to learn to follow Jesus in their daily life.
Jesus talks about the Gospel of the Kingdom all throughout his ministry, for example:
“The time is fulfilled, and the kingdom of God is at hand.” - Mark 1:15
“For indeed, the kingdom of God is within you.” - Luke 17:21
“I have gone [among you] preaching the kingdom of God” - Acts 20:25
“We must go through many tribulations to enter the kingdom of God.” - Acts 14:22
“For the kingdom of God is not a matter of talk but of power.” – 1 Cor. 4:20
“Paul entered the synagogue and spoke boldly there for three months, arguing persuasively about the kingdom of God.” – Acts 19:8
“He [Paul] witnessed to them from morning till evening, explaining about the kingdom of God, and from the Law of Moses and from the Prophets he tried to persuade them about Jesus.” – Acts 28:23
“He [Paul] proclaimed the kingdom of God and taught about the Lord Jesus Christ—with all boldness and without hindrance!” – Acts 28:31
“Now I [Paul] know that none of you among whom I have gone about preaching the kingdom will ever see me again.” – Acts 29:25
They also get easily confused when Paul says:
"I am astonished that you are so quickly deserting the one who called you to live in the grace of Christ and are turning to a different gospel." [Gal. 1:6]