The great big message of the book of Hebrews is the greatness of Christ. It gets that message across especially by connecting who he is and what he’s done to the Old Testament. Our author has one more way he wants us to see the greatness of Christ. He wants to show us the greatness of the Kingdom of Christ, and he shows us this by comparing what Israel received and experienced at Mt. Sinai to new covenant and the heavenly city that we have in Jesus. God has given us an unshakeable kingdom.