If we were immortals, no one would pray and go to church

From which it logically follows that almost no-one goes to church and prays just to thank God for being in existence, but rather he/she goes there in order to beg Him to be preserved in existence.

In our Powers & Perils campaign priest/clerics don't exist, i didn't allow them.
Honestly, there is no such class in the core rules,but Mr. Snider later thought he made a mistake and in a subsequent article appeared in Heroes magazine he introduced the possibility of playing the priest class.

To tell the whole story, in P&P there could be thieves (assassin), it's a skill you can pick (in theory) but i don't allow it as well. In fact, even Richard Snider later realized it was too potent a "class".

But absolutely no priests in my game, for the simple reasons that they just can't have the powers ascribed to them. How many priests in our world see their prayers heard and answered in terms of powers granted to them? Only a few saints happened to have similar powers bestowed on them. In this respect, only Ed Simbalist wrote words of wisdom about the priest class in the past.

To sum it up, in P&P you could theoretically play a priest, a thief, a generic adventurer (let's call it a "would-be warrior"), and a magician. Only for magicians there actually are dedicated chapters in Powers & Perils boxed set, but as i said earlier playing such a character is difficult. Magicians in P&P could lose their own lives when they cast spells.