The Kingdom of God

What is the Kingdom of God? When will or did the Kingdom of God come? What does the Bible say about the Kingdom of God? Why did they need instruction from the LORD? Why didn't they recognize Christ the Messiah when He came the first time? Did Christ cease being God when He took on human flesh and came to this earth? Is the Kingdom of God His church only? Should we be caught up in the times and the season or with Who it is that's coming again? What is the 'mystery of Godliness'? Is the Kingdom of God and the King eternal? Where are the tares and why does the LORD let them grow with the wheat?