Nowhere does the Constitution demand that religion is something that a judge cannot discern. That there will be no “religious test” as a requirement for political office also makes incumbent upon a judge a determination of what is a religion, and what would constitute a religious test.
Your supposedly commonsense observation that Judges somehow cannot determine what a religion is, is not sensible. Neither is disagreement with your statement tantamount to a determination to use the judiciary as the ultimate arbiter of all things.
The specific religious test outlawed by that clause was the one in Pennsylvania that REQUIRED you to be a Quaker to run for office.
Yes, the Quakers were still denying others the right to hold public office right down to 1790, and at that time the NO RELIGIOUS TEST standard was for federal offices only.
No judge needed to determine the validity of Quakerism as a true religion or a false religion. Prohibition of that test was sufficient to eliminate the problem.
Judges, to be equinanimous, must be totally neutral, and even determining if one element of belief or declaration is truly religions is beyond their authority.
The courts have no jurisdiction on how communion is administered nor if the cup is made of gold or silver, or wood. No judge in our system can dictate the number of candles to be lit in a Buddhist temple either on the basis of 79 being truly religious and 80 being a work of demons.
I do believe we still have people who think it's within the jurisdiction of our courts to determine the validity of religious beliefs.
They are wrong!
The USSC and the rest of the system are not a Sanhedrin.
Now, how should a judge deal with something when religion intrudes ~ this is a common situation when you have the Batteling Battlies in court asserting that the other party with joint custody to the children is teaching them about Magic Ferries or Invisible Old men, and vice versa.
Certainly it's going to be the tendency of a judge with some religious upbringing to bring his own (religiously formed) wisdom to bear on the problem. At the same time we have laws, and a reasonably competent judge can use the law to provide guidance in these matters. An incompetent judge can't, and in fact, I'd use the occasion of the mention of "religion" in any court decision as a basis for REMOVING the judge or judges from the bench forever.