So, the way mastery classes work in Last Epoch is that you have access to the bottom half of all three, and can unlock access to the entirety of a single mastery class by completing a quest available in the End of Time town hub. (This choice is permanent.)
As you don’t appear to have chosen the Paladin (or any other) mastery class, the game not allowing you to spend points in passives located higher up in the Paladin mastery class.
I’ve just looked at this in-game, and the game isn’t currently communicating this very well. I’ll speak with the team about ways of clarifying this, however I don’t think we’d be able to make and test any changes in time for the changes to be included in our next update.`
Edit: The numbers for each class are intended to track how many points have been spent in that class, however they appear to instead be showing how high up that class you have unlocked access to. I’ll add this to our issue tracker so it can be...