As Ulric (god of Battle, Wolves, and Winter) is the deity of Physical strength, so Sigmar (patron of the Empire) is the deity of Strength of Will. Priests of Sigmar use hammers, emulating the magic hammer the dwarfs gifted to Sigmar in the days of legend. Priests of Ulric use axes, mainly out of rivalry with the cult of Sigmar. Priests of either cult can be given magic weapons of any type, wear light or heavy armor, carry shields, and may ride warhorses with or without barding.
Warrior priests of Sigmar are fearless defiers of the dark, particularly Chaos, Skaven, and the Undead. They are strong preachers, and any unit they join will Hate the enemy army. Priests of Sigmar can also pray (during the magic phase, counts as bound spells) giving buffs to nearby units or characters- healing wounds, allowing re-rolls, granting ward saves, etc. They also add a die to the Empire dispell pool, representing their patron god's protection against sorcerous powers.
Warrior Priests of Ulric despise weakness and cowardice, and units they join Hate any enemy with a low leadership (6 or less). He also adds a dispell dice, and his prayers have different effects.