Numbers 17:5
And it shall come to pass, that the man’s rod, whom I shall choose, shall blossom: and I will make to cease from me the murmurings of the children of Israel, whereby they murmur against you. And it shall come to pass, that the man’s rod, whom I shall choose, shall blossom: and I will make to cease from me the murmurings of the children of Israel, whereby they murmur against you.
God promised that the rod of the man whom He chose would blossom. That choosing was His appointment to the priesthood, belonging to Aaron and his family. The blossoming sign was given to make the murmurings of the children of Israel cease. Those murmurings were directed against Moses and Aaron.
By divine direction each tribe prepared a rod marked with its tribe's name, with Aaron's name on the rod of Levi. The tribal rods were laid up before God in the tabernacle before the testimony, with blossoming as the token of the tribe the Lord had chosen for the priesthood. The promise was fulfilled overnight, by the next morning, when Aaron's rod for Levi and the house of Levi had budded and produced buds, blossoms and almonds, budding, flowering and yielding almonds in one night.
This miracle established and confirmed Aaron's priesthood and effectually settled the question of who rightfully held it. The rod was shown to the people and afterward laid up in the tabernacle as a witness to succeeding generations. It was kept as a lasting reminder to prevent further murmuring and challenges over the priesthood.