The highest level of altars allows you direct communion with the gods and gives you the ability to call down their wrath or ask them for protection.

By having an Arch-Priest thrall modifying an Altar, you gain access to special crafting options, such as the ability to call on the protection of the gods, or by invoking their wrath in the form of an avatar.

By invoking an avatar, you channel energies into yourself which allow you to become a conduit for the gods manifestation. These manifestations can be controlled by you and while they only last briefly, can wreak havoc upon enemy bases or encampments.