1) THE FORCE OF HABIT
OPINIONS: The teaching of a Tana was repeated before Rebbi Yochanan: if one was reciting the Shema and he forgot what he was reading, but he recalled reciting the verse, "Lema'an Yirbu...," he does not need to return to an earlier point in the Shema. We assume that "his habit took him" and he did not skip anything. What does this mean?
(a) RASHI (DH Sirchei Nakat) explains that from "Lema'an Yirbu" until the end of the Shema the words flow easily. Therefore, if one knows that he has passed "Lema'an Yirbu" but he does not remember saying the words between "Lema'an Yirbu" and the point at which he is now holding, we assume that "habit took him" and he said all of the words between "Lema'an Yirbu" and the point at which he is now holding. He does not have to go back to "Lema'an Yirbu."
(b) The RASHBA argues with Rashi's explanation. According to Rashi, when one is in the middle of reading one of the first two paragraphs of the Shema and he does not know if he said the verses before the point at which he is holding, he must go back to the beginning of the paragraph, since those paragraphs do not flow easily. The Rashba asks that certainly those verses do flow easily to a person, as he is equally, if not more, familiar with the first two paragraphs of the Shema!
The Rashba therefore maintains that when one is in the middle of reading any of the three paragraphs of the Shema and does not know if he said the words before the point at which he is holding, he does not have to return to the beginning of that paragraph, because we assume that he recited it correctly.
The Gemara here is discussing a different situation. The Gemara is referring to a case in which one has just said the verse, "u'Chesavtam Al Mezuzos Beisecha uvi'She'arecha," but he does not know whether he said the last verse of the first paragraph or the last verse of the second paragraph. Normally, he would have to go back to the beginning of the second paragraph, but if he knows that he just said, out of habit, the words "Lema'an Yirbu" after the verse "u'Chesavtam," then we assume that he was up to the last verse of the second paragraph and he may continue from there. (The ME'IRI and RITVA agree with the Rashba's explanation.)
(c) In defense of Rashi's explanation, we may suggest that Rashi means something else entirely. If a person has no idea where he is in the Shema but he remembers saying the verse "Lema'an Yirbu," we assume that he finished the entire Shema out of habit and thus he may continue from "Emes v'Yatziv." This is also implicit in a careful reading of Rashi's words. (Y. SHAW) (If he does not remember saying "Lema'an Yirbu," his lips may have stopped moving simply because they were not sure which "uvi'She'arecha" they were up to.)
HALACHAH: The SHULCHAN ARUCH (OC 64:4) rules like the Rashba.
2) REBBI YOCHANAN'S PRAYER
QUESTION: When Rebbi Yochanan would complete his Shemoneh Esreh, he would add his own prayer for Hash-m's mercy. "May it be Your will, Hash-m... that You don Your mercy and cover Yourself with Your strength...." If Rebbi Yochanan was praying for mercy, why did he also pray for strength ("Oz")? Strength is usually used to bring about justice ("Din"), the opposite of mercy!
(a) The TZELACH explains that the phrase "and cover Yourself with Your strength" really means "and cover Your strength." Rebbi Yochanan prayed to Hash-m to cover His strength (that is, His attribute of strict justice) and thus to conduct Himself only with mercy.
(b) Rebbi Yochanan prayed to Hash-m to activate His strength and use it to suppress His attribute of strict justice, as the Mishnah in Avos (4:1) says, "Who is the strong one? He who conquers his inclination." Rebbi Yochanan prayed to Hash-m to use His strength to conquer His inclination to use strict justice and thus to expose His attribute of mercy. (M. KORNFELD)