Eons ago, there was a war among gods that came close to destroying humanity and the mortal realm. Gods depend on humanity, and their destruction would inevitably hurt them as well. At the conclusion of this war, a pact was signed among the gods to prevent this cataclysm from happening again. Gods can no longer interfere with the realm directly, but they can influence it by using proxies, people who act on their behalf in the function of priests, holy warriors, etc, and are the basis of world religions.
Despite this, there are many dangers to the mortal world. Other realms exist, such as the fae and demon realms, each with creatures hostile to humanity. Invasions occur rarely, but are devastating when they do. Sometimes the invaders are just too powerful or numerous for mortals to handle them.
There exists an ancient spell that is used in times of need. Functionaries of the gods can summon a powerful deity to fight on behalf of humans to help fend off these supernatural creatures. Unfortunately this ritual is so powerful that it takes the lives of the users, and requires hundreds of people to work. They pay with their lives to power the spell and bring a god into the world, and are seen as noble heroes who sacrificed themselves to protect the planet.
The point of making the ritual like this is to show how extreme and serious the situation is and that a high cost must be paid to summon a being like a god to a realm that they shouldn't inhabit. This is an end of world kind of scenario when things have gotten as bad as they can get. However, it brings to mind occurrences like Jonestown or heavens gate, and may come across as cultish. Can it be portrayed in a "noble" light or would this be too problematic?