What is the Kingdom of God?

In mainstream "Judeo-Christianity" the Kingdom is, to most, in the future, and is a utopic place called "Heaven." Some believe it's a place "in their hearts." Many, if not most, have not given it much thought.

How can this be? Jesus preached the Kingdom from the beginning of His earthly ministry. He spoke plainly to His disciples concerning the Kingdom, and spoke a great many parables concerning it.

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