It's in the Constitution.
IT DOES NOT APPLY TO ME. I can make all the religious tests I want and you'd best beware of what I think about people who want to prohibit me from thinking that way.
The Constitution doesn’t tell any of us how to vote or whether or not we can choose to apply a litmus test in picking who we’ll vote for. That’s left up to each of us in accordance to the dictates of our own conscience. Personally I will not apply a litmus test on religion. But I’m not about to agree for giving the government the authority to enforce the prohibition of any voter applying a litmus test of their choosing.