7 was devised by people as were all numbers.
You can argue all you want that they are inherent in reality but even today some cultures use other numbers that aren't arabic.
I honestly don't care about your beliefs in a higher power but please reconsider your 'thought exercise'. A numbers properties can change
on a whim like most other things as they had to be devised in the mind to exist. Even if they haven't in a while, dont write off the
posibility of a shift in mathematical understanding.

Now that my schitzo post is over I have a question. Why are the other religions wrong. Doubt you will read this but if you do
please try to think on that question. You don't want to end up trapped in your beliefs like some people I know.
This is kind of a who asked moment but I have a friend who grew up in the mormon belief system and his life is actually horrible 
because of it so I dont want to see other people become chained by who they decide to follow in regards to the denominations of christianity.


Anyway just know that whatever you believe, even if its wrong its unlikely to affect you so you unless some weird eldritch being 
is running the afterlife o_o