Knowledgeable Christians - What is "The Gospel of the Kingdom of God"?

Jesus instructed his followers to share with others "The Gospel of the Kingdom of God". What is that message? Before you answer, consider these scriptures. Mark 1:14 [ Jesus Begins His Ministry ] Now after John was put in prison, Jesus came to Galilee, preaching the gospel of the kingdom of... show more Jesus instructed his followers to share with others "The Gospel of the Kingdom of God".

What is that message?

Before you answer, consider these scriptures.

Mark 1:14
[ Jesus Begins His Ministry ] Now after John was put in prison, Jesus came to Galilee, preaching the gospel of the kingdom of God

Matthew 24:14
"And this gospel of the kingdom will be preached in all the world as a witness to all the nations, and then the end will come".

When Jesus sent out his disciples to tell others the Gospel, Jesus still had not died for man's sins yet.

Luke 9:5 And whoever will not receive you, when you go out of that city, shake off the very dust from your feet as a testimony against them.”
6 So they departed and went through the towns, preaching the gospel and healing everywhere.

So if the disciples did not tell others about Jesus dying for their sins, What was "The Gospel of the Kingdom of God" that they shared?
Update: Rene O - Nice copy and paste. But I did not ask the diff between the Kingdom of God and the Kingdom of heaven. I already know they are the same.
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