User blog comment:EmpyreanSmoke/Seraphim and "Common" Angels/@comment-25146716-20150228135911/@comment-217.21.232.237-20150313170208

I think with class they mean military rank. Michael is an archstratege, and I'm guessing Naomi took that title when she took over. Does that make Naomi just as powerful as Michael? No. As far as we know, Seraphim could be the title of the person under the leading archangel. Zachariah seemed to be directly under Michael, and he was a Seraph.

After Zachariah died, and Raphael replaced Michael as the leader of heaven Castiel was number 2.