I like the simple idea that if a Good character attacks the Knight, then they turn EVIL.
It is like the equivalent of killing a Saint or even a regular Nun. Not good in the eyes of the Gods.
"But Necrozius", you might ask, "what about the Priest character? Surely HE would be considered holy as well?"
Well, my answer to THAT, my smart-ass friend, is to simply look at the Priest's illustration. He's fat and complacent. He wears the fancy, expensive robes, has the right spells, yes... But he might not TRULY believe. Hence he gets to add ONE to the prayer rolls, while the Knight gets TWO.
Yeah... That's right...
BAM. CASE CLOSED.