The Preacher has encouraged the Hebrews with his litany of faithful saints from the Old Testament who conquered through faith looking forward to the promised Messiah whom these Hebrews now celebrated and worshiped as the Founder and Perfecter of their faith. God wanted a holy people then and still does now. So the Preacher further encouraged and warned them to faithfulness by reminding them how awesome it is to worship the true God.
The Preacher does this by returning to the episode on Mount Sinai some fourteen centuries earlier when God descended on the mountain in smoke with thunder, lightning, trumpet blast, and earthquake. The people were not to come near the mountain, indeed, not even a beast. They went to Moses saying, “You speak to us, and we will listen; but do not let God speak to us lest we die” (Exodus 20:19; 19:1-25). Even Moses trembled at the sight. No doubt the Hebrews to whom the Preacher wrote knew all about this and perhaps wondered what it would have been like to behold that awful spectacle.
But then the Preacher tells them something amazing—quite simply, that what happened on Mount Sinai was child’s play compared to what they experience—compared to what we experience when we present ourselves before the Lord. The passage bears repeating in full: “But you have come to Mount Zion and the city of the living God, the heavenly Jerusalem, and to innumerable angels in festal gathering, and to the assembly of the firstborn who are enrolled in heaven, and to God, the Judge of all, and to the spirits of the righteous made perfect, and to Jesus, the mediator of a new covenant, and to the sprinkled blood that speaks a better word than the blood of Abel.”
So we learn here that when we gather for worship, be it in a grand cathedral in Europe or underground in China, we gather not at puny, earthly Mount Sinai but at the heavenly Mount Zion, the city of the LIVING God, with angels in attendance and saints who have gone before us and who have since been made perfect, and before God the Judge of all and His dear Son. To get a better idea, see Revelation 4 & 5. Our worship sanctified by the blood, not of Abel or a beast, but of the Son of God far surpasses that so long ago. This should rouse two feelings in us: 1) How awesome Christian worship is, and 2) How we should tremble a little more next time we enter the sanctuary where we attend church. We worship a holy God who is a consuming fire. Blessed be the Lamb who makes us presentable.