The second law revealed on this day was the separation of the Levites from among the children of Israel, that they might be dedicated to the sanctuary. "For God elevated no man to an office unless He has tried him and found him worthy of his calling." He did not say, "and the Levites shall be Mine," before He had tried this tribe, and found them worthy. In Egypt none but the tribe of Levi observed the Torah and clung to the token of the Abrahamic covenant, while the others tribes, abandoning both Torah and token of covenant, like the Egyptians, practiced idolatry.
In the desert, also, it was this tribe alone that did not take part in the worship of the Golden Calf. Justly, therefore, did God's choice fall upon this godly tribe, who on this day were consecrated as the servants of God and His sanctuary.