The lamp bearers of the church of justice are the ones holding the pieces of his divine flesh. In particular, it is the captains at the epic rank that are holding the divine flesh.
The god of disaster normally can't find these captains. But if he uses his divine flesh to sense the captains and help the god of disaster to find them, they can kill the captains and weaken the church of justice in a major way.
So this method is something that the god of disaster would be satisfied with and thus, be willing to help him achieve.
And if he promises to help the god of disaster fight the god of justice after he recovers the Ocean of Blood, the chances of the god of disaster helping him should increase.
He could also be wrong about the likelihood of the god of disaster helping him. The god of disaster might just kill him and eat him instead of helping. But this option is the fastest way he can recover his strength, so he is willing to take the risk.
