You have not come to a physical mountain, to a place of flaming fire, darkness, gloom, and whirlwind, as the Israelites did at Mount Sinai when God gave them his laws.
For they heard an awesome trumpet blast and a voice with a message so terrible that they begged God to stop speaking.
They staggered back under God's command: "If even an animal touches the mountain, it must be stoned to death."
References for Hebrews 12:20
Moses himself was so frightened at the sight that he said, "I am terrified and trembling."
References for Hebrews 12:21
No, you have come to Mount Zion, to the city of the living God, the heavenly Jerusalem, and to thousands of angels in joyful assembly.
You have come to the assembly of God's firstborn children, whose names are written in heaven. You have come to God himself, who is the judge of all people. And you have come to the spirits of the redeemed in heaven who have now been made perfect.
You have come to Jesus, the one who mediates the new covenant between God and people, and to the sprinkled blood, which graciously forgives instead of crying out for vengeance as the blood of Abel did.
See to it that you obey God, the one who is speaking to you. For if the people of Israel did not escape when they refused to listen to Moses, the earthly messenger, how terrible our danger if we reject the One who speaks to us from heaven!
When God spoke from Mount Sinai his voice shook the earth, but now he makes another promise: "Once again I will shake not only the earth but the heavens also."
References for Hebrews 12:26
This means that the things on earth will be shaken, so that only eternal things will be left.
Since we are receiving a Kingdom that cannot be destroyed, let us be thankful and please God by worshiping him with holy fear and awe.
For our God is a consuming fire.