Hebrews 12:18-29 provides a great comparison and contrast between Mount Sinai and Mount Zion — two mountains which represent Law and Gospel, Moses and Christ. Both mountains are “awful” in the original sense of that word — inspiring awe in the beholder. That they have in common. But how different they are, as well!
The author’s description of Mount Sinai is taken from Exodus 19-20 in the Old Testament. Moses brought the people to Mount Sinai, which shook and bellowed out smoke deep and dark. Then Moses went up into the mountain alone, to receive the Law from God himself — symbolized in the Ten Commandments written on two stone tablets. This is what it is like to approach God on the basis of our own law-keeping, says the author of Hebrews.
Mount Sinai is physical and earthly (“may be touched” – v. 18). It is foreboding and even terrifying (blazing fire, darkness, gloom, whirlwind, blast of trumpet, sound of words which sent cringing hearers begging to hear no more – v. 18-19), indeed, life-threatening (v. 20-21). Mount Sinai’s portrayal of God is as the Untouchable, the Unapproachable, the Terrible, the Dangerous. To such a scenario, believers in Jesus have not come — although we sometimes behave, and reason, and preach as if we had.