The Mishna on our daf describes how even the performance of a single mitzva can bring good to a person, lengthen his days and guarantee him a share in the world to come, while failing to perform that mitzva brings about the opposite consequences. Our Gemara discusses two specific mitzvot whose performance – according to the Torah – guarantees good and a long life – shilu’ah ha-ken (chasing away a mother bird before taking her chicks – see 22:7) and kibbud av va-em (respecting one’s parents – see 5:15). Rabbi Ya’akov points out that the intention of the Torah must be to guarantee a share in the world-to-come, since he once saw a child who was sent by his father to perform the mitzva of shilu’ah ha-ken, and in the midst of performing this mitzva, the child fell down and was killed. The Gemara relates that this was the turning point for Aḥer (literally “the other,” but here referring to the Tanna Elisha ben Avuya), who turned away from the Jewish religion upon seeing this.
The rishonim point out that according to the Gemara in Massekhet Hagiga (14), Aḥer’s heresy stemmed from a different incident. According to that Gemara, Aḥer 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 (Hagiga 15), Aḥer 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 Aḥer the sense that there existed shetei reshuyot (two competing forces in heaven) – Mitatron and God – which was a common belief of Gnostic sects at that time.
The general approach of the rishonim is that there was more than one cause to Aḥer’s heresy. The Iyyun 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.