A student once came to Rabbi Preida and asked him to teach a particular passage of Mishnah. Rabbi Preida sat with him and went through it slowly. The student did not understand. They went through it again. Still no. Again. Nothing. Again.

Rabbi Preida taught the same passage four hundred times before the student finally grasped it.

When the four-hundredth repetition clicked, a voice from heaven — a bat kol — offered Rabbi Preida a reward. Choose one of two things. Either four hundred years added to your own life, or the promise that you and every one of your descendants will inherit the World to Come.

Rabbi Preida did not hesitate. Give my children the World to Come.

Heaven granted him both. He was given the extra four centuries and the eternal inheritance for his line, because a teacher willing to trade personal longevity for the souls of his descendants had already demonstrated that he understood what a life was for.

Gaster's Exempla (No. 179, 1924) and Eruvin 54b preserve this story. Patience, the rabbis say, is not a virtue for the student only. It is the teacher's ladder to Olam HaBa.