Article VI Clause 3 of your sacred document. Oath/affirmation is required. Book and/or religious belief ain't.
You swear allegiance to the Constitution of the United States of America land, not to a sacred religious text.
It don't matter what book you swear in on. It's the oath to the Constitution that matters.
Check it out (emphasis mine):
"The Senators and Representatives before mentioned, and the Members of the several State Legislatures, and all executive and judicial Officers, both of the United States and of the several States, shall be bound by Oath or Affirmation, to support this Constitution; but *no religious Test shall ever be required as a Qualification to any Office or public Trust under the United States*."
https://constitution.congress.gov/browse/article-6/clause-3/
Keith Ellison (2007) was sworn in on Jefferson’s Qur’an.
John Quincy Adams (1825) used a book of law.
Theodore Roosevelt (1901) didn’t use any book.
And the phrase "So help me God" was specifically not included in the oath, to protect freedom of religion or none. That part's optional.
TL;DR: Don't need to be a Christian or swear on the Bible (or any book) to hold office. In the Rules, dude.
If you disagree you'll have to summon the spirits of the Founding Fathers and take it up with them, I'm afraid.
