What does Hebrews 12:19 mean?

When Israel left Egypt, they were given a covenant by God at the mount of Sinai (Exodus 19:9–20). This event was miraculous and spectacular. It was also terrifying, as God used clouds, fire, the sound of trumpets, and a forbidden mountain to deliver His Words. This passage continues the consistent theme of the book of Hebrews: the new covenant is superior to the old covenant. In this case, the comparison is between how the covenant is presented to us.

The prior verse began to describe the intimidating nature of God's work at Mount Sinai. This depiction continues here, and its effects are given in later verses. The people were understandably shaken, as was God's intent. They were meant to see God as completely holy and One they could not approach in their sinful condition. As explained earlier in the book of Hebrews, the point of the old covenant was for mankind to understand their own sin and to turn to God as a result (Hebrews 9:8–12; Galatians 3:23–24). Another point made in this book is that the old covenant featured various physical components, which turned out to be symbols of the "real" covenant, which was to be spiritual. Here, in this section, a similar contrast is made between the physical events of Sinai and the spiritual nature of the new covenant.