Paladin is a melee class, still built around STR or DEX, but with some degree of casting power which uses CHA. They're considered a "half-caster" compared to the sorcerer "full-caster". Oaths are the subclasses for paladin, like how sorcerer has Wild magic, Storm, etc. Their oaths are a set of tenets they HAVE to follow, and their oath is accounted for in the game. If you do an action that breaks your oath, you become an Oathless paladin (it's not a perfect representation, but the easiest way to think of it is as an evil paladin). I liked the paladin for a first playthrough because of how binding their oaths are to roleplay. I can't just pick the "best" solution to a problem, I have to pick "my" solution.
Oath of Vengence, per the Player's Handbook:
The Oath of Vengeance is a solemn commitment to punish those who have committed a grievous sin. When evil forces slaughter helpless villagers, when an entire people turns against the will of the gods, when a thieves' guild grows too violent and powerful, when a dragon rampages through the countryside – at times like these, paladins arise and swear an Oath of Vengeance to set right that which has gone wrong. To these paladins – sometimes called avengers or dark knights – their own purity is not as important as delivering justice.
The tenets of the Oath of Vengeance vary by paladin, but all the tenets revolve around punishing wrongdoers by any means necessary. Paladins who uphold these tenets are willing to sacrifice even their own righteousness to mete out justice upon those who do evil, so the paladins are often neutral or lawful neutral in alignment. The core principles of the tenets are brutally simple.
If you side with the Absolute in ANY way, you break this oath. Learned that while experimenting early. I wanted to test the game to see if it would actually break my oath, and it does. Freaking awesome. I actually picked it because I was curious what would happen with my companions. Turned out I only had to kill one of them, abomination that he was.