The enemy of my enemy is my friend... Not the most solid of bases to ally with another power in a war, but better to fight two against one than to risk accidentally sabotaging each other's efforts and losing entirely. Besides, religious orders tend to have an excellent reputation among the people, which offers in turn better options for resupplying and acquiring information.

[A part of him considers divine favor as another advantage, but discards it. For all that he cares for Cosmos and Materia dearly, every boon they've given their champions were offset by their role in creating the initial problem.

Elder children turning against their families, though. That gets him to open his eyes once more and frown.]

I imagine the most obvious answer is the correct one, but did he do so of his own will? Out of anger at his own situation, not due to the influence of another, be it direct or through the manipulation of his mind?