Judge Crusader onto the mob to increase your holy damage and crit rate, then use Seal of Command and judge that as often as you can. Most of your damage comes from your weapon though, as Command uses your base weapon damage, so make sure you are using the best weapon you can get your hands on.
You can also increase your damage by picking mainly on demons and undead, as you can get a 3% bonus from the Crusade talent and you can use Exorcism spell for a boost to your damage.