Go Big Or Go Home.

There were a lot of believers who didn't like Supreme beasts in the first place so this was a good opportunity for them to punish one. This way, many people signed up for the army. The army quickly reached 100 million in size. 

The Celestial even compelled other weaker gods to work with him to pressure Legion-5. The army doubled in number because of it. 200 million soldiers were rearing to have a go at the Shadow Of Despair. 

The other Celestials were full of envy as they watched this. They want something like this to happen to them because there is a chance that the Celestial of Light will succeed with his scheme. After all, Legion-5 might buy off the Celestial of Light and Justice if the god proves to be too troublesome to deal with.