Mount Sinai (also called Horeb) is the desert mountain where God met Israel after the exodus. He descended upon it in fire, smoke, thunder, and the sound of a trumpet, so that the whole mountain quaked and the people trembled. There Moses received the Ten Commandments and the covenant law, written by the finger of God on tablets of stone.
Sinai is where a rescued people were given their identity and their calling as the nation of God. The New Testament sets it in contrast with the gospel: Hebrews says believers have come not to the terrifying mountain that could not be touched, but to Mount Zion and the mediator of a better covenant. Sinai reveals God's holiness and the law's demand; Zion reveals his grace in Christ.
Mount Sinai in Scripture
And the LORD came down upon mount Sinai, on the top of the mount: and the LORD called Moses up to the top of the mount; and Moses went up.