Seems to me to be a handy way to have a slush fund - you can’t really spend the cash openly, nor can you store it anywhere that it wouldn’t get exposed by disgruntled employees or found in a search by law enforcement. The money was reported stolen and written off. The checks were in there as a smoke screen (“see, thieves took their whole take and hid it”) to cover for it being an inside job, and if they were found, would be then reported to the insurers.
Not likely that thieves would have done this, though it’s kind of conspicuous to leave a megachurch with a duffel bag brimming with cash and checks, a big enough group of theives would find it easier to sneak the loot out in their clothing than to hide it in a wall.
