Angels are ranked from the lowly lantern archon to the mighty Archangel. As far as power level, archangels are one tier under Cult Powers.
When an angel takes a higher rank, they become more powerful. On worlds strong in negative entropy, ones of Law, this happens by way of judgment of their superiors. For those leaning more towards entropy, the process is random among the potential population. For neutrals, it is less stringent, but still requiring a contest with the rank you seek.