Daf 21. Summary. The gemara continues to attempt to determine which obligations are Scriptural and which ones are rabbinic. Can one infer from Biblical commandments to recite blessings before reading Torah and after a meal that one should recite blessings after reading Torah and before a meal? Apparently not, since the mishnah states that one who has had a seminal emission is not permitted to say a blessing before a meal but is permitted to say a blessing after a meal.
Rav Yehuda holds that the obligation to recite Shema is merely rabbinic. Rav Yosef disagrees. Rabbi Yohanan says, “If only a person would pray throughout the entire day!” Others debate the protocol for continuing or interrupting prayer when one realizes one is repeating a prayer or saying a prayer meant for another time or day. Others seek to establish which prayers require a minyan.
Rabbi Yehuda rules contrary to the majority that one who has had a seminal emission may recite blessings before and after the Shema and meals. The gemara seeks to determine how he derived his ruling. The evidence suggests that he does not derive rulings homiletically through juxtaposed verses (such as ruling that a sorceress is executed by stoning, which is derived from the language in common regarding the sorceress and one who “lies with a beast,” for whom the punishment is definitely stoning). But a case is found where he had ruled homiletically through juxtaposed verses to prohibit a son to marry a woman who has been raped by his father. Since he does rule here on this basis. why not in the case of seminal emissions? Because the verse that was used by others for this purpose had been reserved by him to rule on another matter.
Comment. Three themes intersect in this daf: (1) the distinction between obligations that are rooted in Scripture versus obligations declared by the rabbis; (2) the protocols for rabbinic interpretation when Scriptural sources are not clear; and (3) the threats to purity inherent in sexual drives. All three are major themes that will intersect throughout the Talmud. Here we see the first of the rules for remedying ritual impurity beginning with the implications of seminal emissions and when ritual immersion is required. Clearly, for the rabbis of old, no less for us today, having a penis can be tremendously distracting; indeed, surpassing understanding and beyond justification. At least they don’t deny that these distractions exist. Moreover, they acknowledge the extreme consequences of mismanaging sexual drives in the case of a father who rapes his son’s fiancee. If anything, their acknowledgment that such matters have consequences awards them credibility as they struggle to define the limits of their own authority to regulate themselves and those who would follow them.