You gain another archangel/devil when you earn 7 holy or unholy points on a soul.
So when you can get 7 points on a soul the payoff is big.
As soon as you gain 7HP/UP:
1. The soul goes straight to heaven or hell earning you 3 points
2. No Reap card is required
3. You earn a new Archangel/Devil card, which is worth another 3 VP, and each that you gain allows you to influence another heavenly virtue/mortal weakness in step 1 of the turn order.
You can find this in the rules in the last paragraph of Step 3 under the "Play!" section.
There are some outdated rules linked on BGG so to make sure you are looking at the most current use the link here:
I finished re-reading the rules and was wondering if you only have access to 1 angel/devil card per game. The only time it's mentions that you put one in play is during the setup. In other words, did I miss some mechanic that you can draw and play an angel/demon or is it something that is an effect of other cards.