Symbolism

Angels :

The angels protrayed in Neon Genesis Evangelion don't belong to a special angel order. For instance Sandalphon is one of the highest angels, a twin brother of the Seraphim Metatron. Sahaquiel is ruler of the 4th heaven, while Samshel is a Grigori. So the obvious assumption, that all of them maybe are fallen angels and thus maybe hostile to mankind, is wrong. But there is indeed something.

In the Qaballah, angels are associated with certain forces of nature (like rain or hail). One could pray to (enchant ?) angels for advice, to relieve labour or receive mental strength. Angels were "assigned" to the 7 days of a week, or even the hours of a day. These assignments were taken into account in how these angels look in Neon Genesis Evangelion, or when and how they first appear.

For instance Bardiel (Angel of hail/lightning). He is a parasite who infects Unit-03. This happens, though not explicitly explained as what it is, when Unit-03 is transported via airplane. The plane flies through a cloud and is hit by a lightning ! A similar,maybe more or less obvious allegory, could be found for every of the 18 angels.