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.