I can't understand the logic of such a requirement.
For the purposes of an essay on "Religion and its Place within the Government" I think a quality essay could be written without referencing "God".
To not use the word would hardly force any student to write that religion is unjustifiable. In fact, I don't see how the justification of religion per se would be an issue one way or the other. It's not what the topic is.
So no, I don't think the instructor's logic is transparent. I still don't understand it.