What does Numbers 33:38 mean?

Aaron the priest died on top of Mount Hor, just as the Lord had said. This happened in the fortieth year after the Israelites left Egypt, on the first day of the fifth month. Numbers 33:38 - Modern Text Bible

(This verse marks the death of Aaron, Moses' brother and the first high priest, as a significant event in Israel's journey. The timing shows how long they've been wandering since leaving Egypt.)