[Update 18-04-2020]
This class has been renamed Knight to better reflect it's unique nature in comparison to the classic D&D-ish Paladin.
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TL:DR

I am dissatisfied with the way most games portray the Paladin class/archetype. Often, not always, but quite often, the Paladin is built in a way that encourages an obnoxious holier-than-thou play style. I've seen oh so many Players bring to the table characters that can only be described as heartless abusive zealots because the game mechanics frame whatever a Paladin does as being "right & just" by default.

The Tricks of an Old Dog

I could rant about the real-life psychology behind feeling justified for being a jerk. But instead I'll skip it to dive straight into game design. You're welcome.

The main inspiration for the FW Paladin, although I only realised this after the fact, is a concept at the core of Dogs in the Vineyard, yet another seminal game by Vincent Baker. Dogs is a game that focuses on exploring themes of morality and justice. It does so in many different ways that I won't go into detail now, but a key element is that it does not define mechanically what is moral and what is not. Players get a bunch of vague, contradictory and controversial fluff about what "a true dog of the Lord" should do and be, but no rules. The rules are meant for everything else, but not that. The game asks a question, and does not offer an answer. This absence, this void, it is the open space that allows Players to explore what they think is moral, right and just during active play.

Fantasy World is obviously a different game whose aim is to instead engage the Players with stories of adventurous drama. But is there a way to apply some Dog tricks to make the Paladin more interesting to play?

Mirror Mirror on the Wall

Dogs employs a whole game system to position the Players in just the right way to help them explore questions of morality. A simple selection of Class Moves can't possibly accomplish the same result, but it also doesn't have to; as we said FW's scope is different. It just needs a smaller, adventurer-sized version of it. Knowing this, the method employed to make the Paladin work was to create the aforementioned fruitful void... and then stick a mirror in it to, less subtly but more quickly, produce a Dog-like effect.

First of all, the FW Paladin has no direct divine element. They can be devoted to a religious cause, but just like the Cleric they don't have any reassurance from the game mechanics that what they believe is true or right. The Paladin acts on behalf of other mortal people be they the kingdom monarchs, the church priests or the leaders of their own order. This is important because it removes the safety of having a superior and external system of values: others might tell you what is right and wrong, but they are no God, no all-knowing being, just other people like you. Whatever you chose to believe, and to do, is your own responsibility.

The game also carefully shies away from offering an opinion or judgement of its own about such matters. In the core Paladin move A Knight in Shining Armor the choice selection for the absolute value does not adhere to any moral paradigm. Instead it plays on the neutral idea that one can get power over a thing by renouncing it; it smells of cosmic balance but it's a theme often found in knightly/chivalric stories and says nothing about what is right or wrong to do in life.

Burning Faith, Ever Onward, Hospitaller, Moral Compass and Quest are all moves that grant the Paladin great power at the "cost" of asking the Player to be explicit about their actions, asking time and again why something is right and just and honourable. This way, bit by bit, the Paladin's Player will express in very concrete terms their own ideas about what are honor and morality. This alone is already very valuable. Partly because things tend to be veeery different when they are silent actions then when they are spoken words.
Partly because this is invaluable material that the World can and should use to explore and test all the interesting things that the Paladin spouts about honor and valor and such stuff. The rulebook even takes the time to remind the World of this task/opportunity:

A Word to the World
It is always the World's job to take note of interesting things the Protagonists say and do in order to reincorporate them in later play. So why do some Paladin moves say "the World will make a note of this"?

For the Paladin, it adds pressure: what you believe matters and will not be left unexplored.

For the World, it is a gentle reminder: a major point in the unique fun of playing the Paladin is to be confronted with your own bullshit. The Paladin constantly expresses what they think is right, just and honorable, and the game doesn't judge it. But it tests it. So it reminds the World to take extra notice of it: XYZ is good? Fine, but is it still good when others do it too? Or do it to you? Or do it for reasons you dislike? Or do it in a way you dislike? How do you handle an enemy you deem moral? How do you handle an ally you deem immoral?

The other moves then round up the character by leaning on the classic archetype of the chivalric knight.
Voice of Authority and I Am the Law grant them charisma and authority.
Aegis of Valor and Knight's Mount add stereotypical touches that match the expectations of most people.

The Gift of Choice

In final analysis a Player taking up this new Paladin will still be able, if they so wish, to play an abusive sanctimonious jerk. The difference is, this time it will happen in a way that will enrich everyone's play experience and story, rather than ruining it. And more importantly, it will be a Player's choice; the game will help them clearly see and be aware of what their Paladin's beliefs and behaviour are, what they mean for the people around them, what cost they carry. With no judgement and no hidden lessons, but a light over all the things that were previously taken for granted. From there, it's the Player's exclusive privilege to do as they feel is right ;)