“Hey guys, I found it: why it had to be Cas! The third ingredient!”
Part 1 (based on this theory)
Something I noticed about the ingredients for Metatrons’ spell
The Nephillim is the product of love, angel and human love but love nonetheless.
Cupid’s bow? Well, that is a bit obvious don’t you think? It is the creation of love. It makes love and spreads love.
I think you know where I am going with this. Cas’ grace, being Cas’ essence and whatnot, is in love and could very much be just love itself; Samandriel did say that he thought Cas had too much “heart”.
Love is what made the angels fall.
Also Cas was a seraph and in general angel lore I believe they’re made out of pure light and love for God.
Let me present to you a thing
seems legit.