God includes His entire universe, even beyond the bounds of this earth. So the Kingdom of Heaven is in the Kingdom of God. Matthew is applying God’s rule specifically to this earth. Mark is reaching out and including a wider area because the Kingdom of God includes the entire universe with all of His creatures. As far as the earth is concerned, to say “the kingdom of heaven is at hand” or “the kingdom of God is at hand” would be synonymous. But the Kingdom of God would include regions beyond the