One of the more dramatic moments in Final Fantasy IV is Cecil's transformation from a Dark Knight into a Paladin. The game is very literal with its story of redemption, and from the moment he assumes his new class, the way he acts changes. Gone is the questioning, unsure, spoony-bard slapping, in his place there is a girly-looking no-holds-back hero.
Of course, I think he was a hero before then.
In the earlier installments of the Final Fantasy series, characters are defined by their job class. After Final Fantasy V, a character's job class began to have less importance, and in say, Final Fantasy VII, a character is defined more by their limit break. In recent installments, the class system has had a revival, both Final Fantasy X-2 and Final Fantasy XI rely heavily on class. Still, no characters are as heavily defined by their class as they are in Final Fantasy IV.
When Cecil begins his journey, he is a Dark Knight, a class based on offensive power. Though he is as tanky as it gets during the first part of the game, his special skill is geared towards offense, and he is certainly the most consistant damage dealer in the party. The Dark Knight's special ability is called "Dark Wave" or "Darkside" in later installments. Cecil hits all enemies onscreen with a powerful attack at the cost of his own HP. This hints at the ultimate futility of Cecil's existance as a Dark Knight. Nothing truly evil can be overcome by a Dark Knight, in the end they destroy themselves. I know I've darked Cecil to death on more than one occasion.
As hints are dropped and swords are given, Cecil makes his way to Mount Ordeals in order to hopefully become a paladin. The tests are hard, and no one has ever successfully completed the trials. Cecil reaches the top and must literally defeat the dark half of his soul. The Mysterious Voice From Beyond has only one thing to say.
"The true paladin will sheath his sword."
The only way Cecil can overcome his darkness is to forgive it. To reconcile with it. This is, in the wake of Kain, the most final and definite peice of wisdom Final Fantasy IV has to offer us. Cecil alone, of all the characters strugling with their concscience, has managed to find peace with themselves. And it's only through accepting his dark half that he's able to become the rock that the party looks to for support.
As a Paladin, Cecil has much more HP and access to a limited amount of white magic spells. His special ability is "cover" which prevents damage being done to a single target at the expense of Cecil's HP. (He basically jumps in front of the party member and takes the damage himself.) Cecil will also automatically cover party members who are critically wounded. In this incarnation, he is perfectly geared for defense, although he's still a pretty solid fighter.
For all his strife and wardrobe woes, Cecil is rewared with the ability to use the power of the crystal to defeat Zeromus, the darkness which lurks in men's hearts personified. He alone posesses the purity of heart necessary for this task.