Q: I attended a Shabbat meal and I noticed that at the end of the meal right before benching (the after-blessing) some of the people took water, poured it on their fingertips, and then wiped their lips. What is going on there? Is this some kabbalistic custom? I’ve heard of washing before the meal but never at the end of it!?
A: What you observed is called “Mayim Achronim.” Its source is in the Mishna and the reason for it is that people used to eat with salt called “Melach Sdomis” which, if it came in contact with the eyes, could cause blindness. The Rabbis therefore said that before one ends the meal you should wash your hands to get rid of any of that salt that was left on the fingers.
Today we no longer use that salt, but the accepted custom is that we continue to practice this ritual. The reason for that is that many of the rabbinic enactments have a reason that we were told but there very well be other deeper reasons as well. Therefore, even if the obvious reason no longer applies, we continue with it knowing that our great sages had divine wisdom and that every part of Torah is eternal.