On the first day of the third month since leaving Egypt, Israel camped at Mount Sinai.
After a long journey from Egypt, nearly 90 days later, Israel reached Mount Sinai in the Arabian desert. It may have seemed like just another waypoint at first, but it would soon become the most impactful period in the foundation of the nation of Israel. For this is where GOD offered Israel His covenant of exclusivity, and this is where Israel's law, the Law of Moses, was given.
1 Now in the third month after the children of Israel departed from the land of Egypt, on the same day, they came into the Sinai Desert. 2 For they departed from Rephidim, came into the Sinai Desert, and camped in the desert. So Israel camped there before the mountain.
(Exodus 19:1-2 OSB)
Additionally, this fact is worthy of its own Biblical Principle because of later Scripture's allusion to these events as a shadow pointing towards future happenings.