This is a good idea. Here is the problem with it.
Because of the fluctuation in the price of Bitcoin, religious leaders wold have to make agreements with the people they send bitcoins to, that the money be based on Bitcoin value rather than fiat value.
In the real world, most religious leaders (right along with everyone else) base value on fiat. Thus with the fluctuation, nobody knows exactly what value he is getting or giving if he uses Bitcoin.
If Bitcoin becomes a leading currency, fluctuation might level off.