We already have paladins, so I don't understand why we should have "armored warriors of faith" and "heavier armored warriors of faith".
I see this coming up again and again. There is a great deal of ground in which the three classes can be separated. Kevtar already gave a very good explanation, yet it doesn't match up with my own imaginings. So for what it's worth, here are my feelings on the classes:
○ A paladin is a chosen weapon of the gods. Their calling is impossible to ignore. A cleric may feel a calling, but takes the choice to become a divine warrior. Likewise the priest may feel a calling, but still has the option to lead a normal life rather than taking holy orders. The paladin has no choice in this.
○ A paladin is taught the skills most appropriate to one of their calling, typically this means martial combat. A cleric blends martial combat training with training in holy prayers (particularly those that compliment their martial abilities). A priest is taught only holy prayers, and gains significantly more power in them than the cleric.
○ A paladin receives most of his magical abilities through holy blessing. He can channel divine power, but has little control over it. A cleric can channel divine power and has moderate control over it. A priest can channel divine power, bending it to his will at a moment's notice.
○ A paladin's magic tends to be focused on himself (buffs), his enemy (smite), or those other than himself (lay on hands). He cannot re-direct these abilities. A cleric's magic is focused on support and healing. A priest's magic covers support and healing whilst also being his primary form of combat power (ala invoker/laser cleric)
