Unlike human beings who share a common nature, St. Thomas Aquinas teaches that as pure spirits each angel has a unique nature. Their degree of likeness to God and His Divine Spirit distinguishes them, rather than the material differences which permit us to identify individual human beings. Nonethless, they can still be classed into groups, called choirs, according to their spiritual similarity to each other and the missions which God has given them. Closest to God are the spirits of the highest choirs, the Seraphim, Cherubim and Thrones; closest to mankind, and most like us in spirit, are the lower choirs. Among these are the archangels and angels, who serve as greater and lesser messengers (Greek, aggelos) to human beings from God. We have the names of three of the seven arch-messengers, Michael, Raphael and Gabriel in the Sacred Scripture–St. Rapahel identies himself as one of seven who stand before the throne of God (Tobit 12:15). The names of the other four archangels are not given to us to know, and the Church forbids us to call upon by name any but the three whose names Scripture has revealed. St. Thomas Aquinas gave us the following hierarchical list of the nine angelic choirs and using the traditional names from the Hebrew and Greek through the Latin Vulgate of St. Jerome): Seraphim (Is. 6:2, 6, seraphin)Cherubim (Gen. 3:24, Heb. 9:5, cherubin)Thrones (Col. 1:16, throni)Dominions (Col. 1:16, Eph. 1:21, dominationem )Virtues (Eph. 1:21, virtutem)Powers (Rom. 8:38, Eph. 1:21, potestatem)Principalities (Col. 1:16, Eph. 1:21, principatum)Archangels (Rev. 12:7, Jude 9, archangelus)Angels (over 300 references, angelus) READ MORE