Rabbis find themselves quite embarrassed when congregants come to them and say, “What I am telling you, rabbi, is not only true, but I swear it on the life of my grandchildren.”
The rabbi is likely to reply, “If it is true, then let it be true on its own merits; leave your grandchildren out of the discussion, and leave out the oaths.”
An alternative scenario might be, “Rabbi, what I’m telling you is the emess, and I’ll swear it on the Sefer Torah.”
Again, the rabbi will probably say, “If it’s as true as you say, you don’t need to swear any oaths, on the Sefer Torah or anything else.”
What right do rabbis have to reject the offer to take an oath?
There is a principle, Afilu al ha’emet ein yafeh l’hishave’a – “It is not right to swear an oath even on the truth” (Tanchuma Vayikra 7). The truth has to stand on its own feet.
A person who blurs the distinction between truth and falsehood will not get away with it for ever. If they tell a lie, an oath will not make it kosher; if they tell the truth, an oath is not necessary.