Alright this topic will summarize the roles of the different stats you have, so as to make things clear.
Constitution:This stat represents a person's physical endurance. It will be used for HP, and also in situations where you need to resist physical harm. It's essentially how durable you are. It's used for skills that have you doing physical activity for a long time.
Power: This is of course your physical strength, it's used to determine how much strength you can put into things physically. Used for skills that need brute strength to get through.
Knowledge: This is your mental strength and how powerful your mind is of course, it's also used for alot of talents that require thinking.
Will Power: This is a representation of your mental fortitude, and shows how resilient your mind is. This will be used for prevent mental attacks mostly, or for skills that take alot of focus and a long time.
Dexterity: A measure of how coordinated your body is, not exactly how fast you are, but it's used for that as well. This is used for evading, and doing complicated and intricate activities.
Perception: One's awareness of their surroundings. Used primarily for sensing skills and weapon proficiencies without this you'll be takin' shots in the dark.*chuckle*
Luck: This is a display of how fortunate your are, there is no direct battle correlation, but that doesn't mean it wont be used in strange situations.
Charisma: A measure of one's presence and appeal strength (be it good or bad) again there is no direct battle relation, but alot of skills that involve working with people use this stat.