Block is a defensive attribute, and affects a character’s ability to mitigate physical damage from incoming attacks using a Shield. To benefit from Block, characters must have a Shield equipped, and depending on the attributes of the Shield, characters will block more or less damage. Characters with more Block will receive less damage when they block a physical attack.
Templars tend to have the most Block of all the classes because of their extensive use of the Shield when playing the role of tank or protector.
A high Block attribute is important for classes that use Shields to mitigate incoming physical damage, though all classes that use Shields can benefit from more Block.