Angels-CHOIRS

In the ancient Western world, particularly medieval Europe, it was
believed that angels were arranged in hierarchical order. Perhaps
because the angels were believed to continually sing the praises of God,
the levels of the angelic hierarchy came to be referred to as choirs.
In the schema of the early sixth-century theologian Dionysius
the Areopagite—a highly influential outline that was later adopted by
Thomas Aquinas—the angels are arranged into nine choirs, which
are grouped into three hierarchies (perhaps reflecting the Trinity). In
descending order of closeness to God they are:
First Hierarchy Second Hierarchy Third Hierarchy
Seraphim Dominions Principalities
Cherubim Virtues Archangels
Thrones Powers Angels