I always wondered what effect these two things have on the game. I know higher firepower makes units more effective against unfortified targets but that's all I know.
"Hit points represent a unit's relative durability in combat situations"
"Firepower indicates the number of points of damage that a unit does each time it successfully scores a hit"
Think of a boxing match consisting of rounds.One fighter is a power puncher.The other is a pugilist.The power puncher can do as much or more damage with 1 shot than the pugilist can do with 5 or 6.