Kingdom of God

Thinking hard yesterday about this ... something in B. McLaren's new book:

Jesus on the earth, speaking and teaching about the Kingdom of God. But what is the Kingdom of God?

Is it heaven ... the place for us after we leave the earth?

Or is it a system - a lifestyle, governance, value system - that is to be enacted and lived out on earth. Right now.

Could it be both? Is every mention of the Kingdom of God either one or the other? Always one or the other?