This is far more trustworthy than a simple guarantee, as this method of preaching truly embodies the style of Lady Strategy, which other deities find hard to replicate.
Since the other party has spoken thus, he naturally wishes to reciprocate, despite having already a clear plan for his ascension to godhood, he does not need belief in this aspect.
"You don't need to do this deliberately." Katherine's smile grew more apparent, "You seem to have not fully adapted to the new identity bestowed upon you by the Lady. You are her Chosen, and when you present a revolutionary new tactic, do you think the world will credit you with this honor? Or the Lady?"
