One of the nine ranks in the hierarchy of angels mentioned in Holy Writ. According Isaiah’s vision, seraphim have a human form and six wings: two wings cover their faces, two wings cover their legs and two wings fly. Seraphim encircle the throne of God and cry continuously: “Holy, holy, holy, is the LORD of hosts: the whole earth is full of his glory” (Isaiah 6:2). According to the angelic hierarchy described in the book of Pseudo-Dionysius the Areopagite Celestial Hierarchy seraphim are the highest rank (seraphim, cherubim, thrones), closest to God.
They are also depicted on the key-stone of the arch of the eastern vault and on the soffit of the altar’s window.