For hundreds of years now, numerous Christian theologians have helped construct a hierarchical order for all of the Biblical angels. This complex organizational system was mostly devised in the medieval era, and is commonly referred to among Christian scholars as the Angelic Choirs.
One of the most predominant and renown classification systems was published in the 4th and 5th century by Pseudo-Dionysius the Areopagite, and was entitled The Celestial Hierarchy. In the centuries to come, this book would act as a cornerstone for extensive expansion and refinement of the angelic orders, with some derivative works more or less picking up where Pseudo-Dionysius left off, while others started completely new tangents, or even contradicted the author's primary conclusions. For example in the Middle Ages theologians placed the archangels and angels at the lowest point in the hierarchy, with their reasoning being that these ranks of celestial beings were almost exclusively involved in the affairs of mankind, and thus were furthest from God. Many conclusions like this one and others, though different but entirely derived from The Celestial Hierarchy, would go on to be recognized as the new academic standard.
The highly influential works of both The Celestial Hierarchy and it's predecessor the Summa Theologica, were for the most part built up around the New Testament scripture of Colossians Chapter 1, verse 16, and Ephesians Chapter 1, verse 21. Obviously Old Testament Biblical scripture played a role as well, especially with regard to establishing the first sphere of angels, however it was mostly through New Testament sources that early Christian theologians were able to piece together three angelic hierarchies, spheres, or triads of angels, each containing three choirs or orders.
