He did even like The Order. I'm guessing he only stuck with it for Kyrie. He seemed happy taking them all down.
That's something else. I would have found Credo's losing faith in The Order better if it had not revolved around Agnus and Sanctus using Kyrie. What about the fact that Sanctus got Agnus to make hell gates, set demons on the town and then have the Saviour statue show up to make it look like they saved the day.That's reason enough to lose faith.
So basically the plot was about a crazy old guy who wanted to make more followers for his religion by saving them from a problem he caused.