http://revach.net/article.php?id=4437

Section: Parshas HaShavua   Category: Story
Parshas Ki Sisa: The Chofetz Chaim To Rav Shimon Schwab - Answer The Call!
Rav Shimon Schwab told over the story of the time he went to visit the Chofetz Chaim.  The Chofetz Chaim asked him, "Did you know that I am a Kohein?".  Rav Schwab answered, "Yes".  The Chofetz Chaim then asked, "Are you a Kohein?"  Rav Schwab said no.  "What about a Levi?"  "Also not", said Rav Schwab.

"What a pity", said the Chofetz Chaim.  When Moshiach comes everyone will yearn to do the Avodah but "V'HaZar HaKarev Yumas", any non Kohein or Levi who do an Avodah will be put to death.

I will do the Avodah and you will not because when Moshe screamed Mi Lashem Eilai, my grandfather went running to join him, while yours did not.  Because of this all their descendants lost the chance to participate in the Avodas bais HaMikdash for all generation.

Concluded the Chofetz Chaim, in your life when you hear the call Mi Lashem Eilai, who will stand up for Kavod Hashem even before a hostile crowd, you must go running.  If you don't you will lose out forever.