Rabbi Yohanan teaches that fulfilling the mitzva of ma’aser guarantees wealth. He derives this from the passage (Devarim 14:22) asser te’aser – a tithe shall you tithe – which he understands to mean asser bishvil she-titasher – separate tithes so that you should become wealthy. At first glance this appears to be a simple play-on-words, switching the Hebrew letter sin for a shin, thus changing the pronunciation of the word from asser (tithe) to osher (wealth). Others explain that this is a more straightforward interpretation of the pasuk — separate tithes, and by doing so you will be given the opportunity to separate yet more tithes (i.e. you will see success in your endeavors).
Rabbi Yohanan found the son of Reish Lakish. He said to the boy: Recite to me your verse, i.e., the verse you studied today in school. The boy said to him: “A tithe shall you tithe.” The boy further said to Rabbi Yohanan: But what is the meaning of this phrase “A tithe shall you tithe”? Rabbi Yohanan said to him: The verse means: Take a tithe so that you will become wealthy. The boy said to Rabbi Yohanan: From where do you derive that this is so? Rabbi Yohanan said to him: Go and test it.
The child responds that testing God is forbidden, quoting the passage in Devarim (6:16) that clearly forbids testing God. To this Rabbi Yohanan responds by quoting Rabbi Hoshaya as teaching that tithes are unique because of the pasuk in Malachi (3:10) in which God clearly allows the Jewish people to test him with regard to the mitzva of ma’aser, promising to open the storehouses of the skies to those who keep the mitzva properly.
The exchange between Rabbi Yohanan and Reish Lakish’s son is interesting because Reish Lakish was married to Rabbi Yohanan’s sister, making the young man Rabbi Yohanan’s nephew. We know that Reish Lakish had a number of children – sons and a daughter. The child in this story appears to be seven or eight years old, but it is clear from the conversation that he was a sharp young man. None of Reish Lakish’s children are quoted as adults in the Talmud, which leads to speculation that none of them survived to adulthood.