In this radiant icon, we see Moses and Aaron standing within the Tabernacle of Witness. Moses holds a chalice and a text of the Law, while Aaron the high priest holds a censer and the budded rod.
The orb with the seven-branch candle stand contains an icon of the Theotokos, because she is the fulfillment of many of the Old Testament's sacred symbolism. As it says in the Synodikon of Orthodoxy from the Seventh Ecumenical Council: "the rod and the tablets, the ark and the lamp, the table and the altar all depicted in advance and prefigured the All-holy Virgin Mary, the Mother of God."
This Mosaic altar was also, in another sense, a foreshadowing of the altars of the Church. The Ark of the Covenant contained three sacred objects: the Tablets of the Law, the jar of Manna, and the Rod. The three principal items on a church altar correspond to these: the Gospel, the tabernacle of the consecrated Eucharist, and the Cross.