"As Waldemar said, in the US it's a normal legal term used to refer to acts such as earthquakes, tornados, floods, etc that are not caused by any human act or lack of action, in other words, Mother Nature throwing a tantrum. "

I can see where your coming from, but with these kind of contractual agreements, and with the emotional attachment of what we do, especially the religious nature of it, you can bet your back pocket that any legal proceedings will be more for the protection of the client as opposed to your own protection.

An agreement is just that, an agreement between 2 parties.
If one party doesnt read it, or doesnt understand it, they shoudlnt sign it. By signing it, theyre stating that not only have they read the agreement, but theyre also stating that they understand it AND they agree with it.
The difference though, is how it may be percieved, which is a matter of conjecture, however in the end, if your agreement is vague, this conjecture can be questioned, which is something u dont want.