This skill has a hidden bonus to max resistance. It does not display on the skill itself (for space reasons) but it will display on your character screen.
For each point in the skill you, and your nearby party members and pets, will receive +1% to maximum resist. This is capped at 95%.
The Paladin also receives half of the +max resistance bonus (rounded down) when the skill is not active. So with 20 points in the skill you will get +10 to maximum resistance when the skill is off.
You get no passive resistance to your actual resist but just to your maximum resist. Items that give bonuses to skills do not increase the passive bonus.