It's more restrictive than that, actually. Each angel has a certain bloodline that can be claimed as a vessel. This particular vessel was my only adult option at the time I needed one, but fortunately he suits me well.

[He smiles, then, amused rather than offended.] Darling, there are hundreds of thousands of angels in Heaven, and only three ever mentioned by name in the Bible. I wouldn't expect you to have heard of me.

I'm not the only angel here, either. In fact, we have archangels, which outweigh my abilities considerably, and even they can't manage an easy escape. Whatever's got us here is extremely powerful.