This summary is not the rule. The rule text controls.
This rule says that a witness's religious beliefs cannot be used in court to attack or boost their credibility. Lawyers cannot ask a witness about their faith, or lack of faith, just to convince the jury that the witness is more or less trustworthy because of it.
The idea behind this rule is fairness. What someone believes about religion does not tell you whether they are honest or reliable as a witness. Courts want juries to judge credibility based on things like the witness's testimony, behavior, and any actual evidence of dishonesty, not their personal religious views.
This does not mean religion can never come up in a trial. If a person's religious beliefs are actually relevant to the facts of the case, that is a different matter. This rule only blocks using religion as a way to make a witness look more or less believable simply because of what they believe.
