Masechet Hullin closes with a Mishnah that relates how the passage regarding the mitzvah of shilu’ah ha-ken teaches that fulfilling this simple commandment guarantees a good and lengthy life (see Devarim 22:7.)
In fact, there is another mitzvah that offers a similar promise – kibbud av va-em (respecting one’s parents – see Devarim 5:15) also includes a clause guaranteeing that “your days may be long, and that it may go well with you.” Rabbi Ya’akov, however, argues that in making these statements the intention of the Torah is to guarantee a share in the world-to-come. This teaching was based on his own personal experience. Once he saw a child who was sent by his father to perform the mitzvah of shilu’ah ha-ken, and in the midst of performing this mitzvah, the child fell down and was killed.
The Gemara in Masechet Kiddushin (daf, or page 39b) relates that this was the turning point for Aher (literally “the other,” but here referring to the Tanna Elisha ben Avuya), who turned away from the Jewish religion upon seeing such a situation.
The rishonim point out that according to the Gemara in Hagigah (14), Aher’s heresy stemmed from a different incident. According to that Gemara, Aher was one of the arba she-nikhnisu ba-pardes – four tanna’im who embarked on the study of esoteric secrets of the Torah. According to the Gemara (Hagigah 15), Aher peered into heaven and found the Archangel Mitatron who had received permission to sit down to write the merits of the Jewish people. From the midrashim it appears that Mitatron is the angel responsible for the entire world, and seeing him gave Aher the sense that there existed shetei reshuyot (two competing forces in heaven) – Mitatron and God – which was a common belief of Gnostic sects at the time.
The general approach of the rishonim is that there was more than one cause to Aher’s heresy. The Iyun Ya’akov suggests that his experience in the pardes led him to question certain of his beliefs, but he still remained a practicing Jew with the hope that he would receive reward for his actions. Upon seeing the incident described in our Gemara he lost faith in heavenly reward and punishment, and rejected Judaism entirely.