Sefer Otzar Yisroel relates that the Me’or Einayim once came to a certain city and discovered that there was no local mikvah. When he asked why the town had no mikvah, he was told that it was because the city was located on top of a hill and they would have to dig very deep to find water. The residents of the city were very poor, and they couldn’t afford to pay for such an operation.
The Me’or Einayim wouldn’t accept this excuse. He kept asking how it could be possible to raise the money to make a mikvah. Finally, he was told that there was one rich man who lived in that city. This man had the ability to pay for the entire mikvah but he refused to do so.
The Me’or Einayim went to see the man and asked him to pay for a mikvah. The man said, “If you would give me your share in Olam Haba in exchange for the money, I will pay for the mikvah.”
The Me’or Einayim said, “Every day, I recite Kriyas Shema and promise to serve Hashem ‘b’chol m’odecha’, with all of my resources. What resources do I have? All I have is my portion in Olam Haba! I must be willing to give it up to build a mikvah.”
And the mikvah was built.