At Mount Sinai, Israel promised to obey God.
After GOD finished instructing Moses at the camp of Mount Sinai, Israel reaffirmed their commitment to obey GOD:
1 Now He said to Moses, “Come up to the Lord, you and Aaron, Nadab and Abihu, and seventy of the elders of Israel, and worship from afar. 2 Moses alone shall come near to God, but they shall not come near; nor shall the people go up with them.”
3 So Moses came and told the people all the words of God and all the ordinances, and all the people answered with one voice and said, “All the words the Lord spoke we will do.”
(Exodus 24:1-3 OSB)
At this point, the covenant—a multi-party agreement—was settled. GOD had given Israel the terms of the covenant along with some basic instructions and promised blessings for keeping the covenant and curses if they should break the covenant.
Moses reported the terms of the covenant to Israel.
Israel accepted those terms.
Thus the deal was struck. The only thing left was to seal the covenant, which came next.