When Moses entered the tent of meeting to speak with the Lord, he heard the voice speaking to him from between the two cherubim above the atonement cover on the ark of the covenant law. In this way the Lord spoke to him.
At that time the Lord set apart the tribe of Levi to carry the ark of the covenant of the Lord, to stand before the Lord to minister and to pronounce blessings in his name, as they still do today.