I really don’t understand all the conspiracy theories here. As plenty of others said, the church doesn’t need to commit insurance fraud to make a couple hundred thousand. They just ask for it and the flock gives it. And Osteen himself has a million places to hide “go money” that are more legal and more accessible than the bathroom wall inside the church. In addition to the safe deposit boxes and opaque investments that @anonotwit mentioned, there are probably a lot more accessible hiding spots in his $10.5MM house (I mean, parsonage), or his other $2.9MM house. Plus the checks (which are presumably a significant share of the $600k) are largely worthless as they’ll mostly be stopped once people here that the collections were stolen.
This was almost certainly a classic crime of opportunity. Some low level staffer or volunteer found himself or herself (the gender of the bathroom will probably tell us which, since I don’t believe this is a trans-friendly congregation) alone with a pile of collection envelopes, swiped them and went into a bathroom so they could think behind a closed stall door and nobody would ask what they were doing. While there, they figured out a way to push the money into the wall. Maybe they planned to come back for it later once they figured out how to retrieve it. Or maybe they had second thoughts about stealing from a church and just decided to dump their loot (no matter how grifty the church is, the people who work/volunteer there probably believe that Jesus frowns on theft). But I’d be willing to wager that there is some sort of vent or other opening in that wall through which envelopes can be pushed.