Reading Shema as Kriat "Keva"
An interesting halakha surrounding recital of kriat shema may emerge from three different gemarot. Each gemara discusses a different feature of shema recital, and interestingly enough the gemarot do not cross reference each other. Yet several Rishonim do link the three and deduce a halakha about kriat shema that requires these various parameters.
The gemara in Berakhot (13b) demands that shema be recited when one is stationary, as opposed to walking or traveling and subsequently, records a debate as to how much of shema requires stationary recital. However, the Gemara does not explain WHY shema must be recited while stationary. Many Rishonim (Rashi, Tosafot, and Ba'al Ha-Ma'or) assume that a stationary recital will allow more focused KAVANA, which is absolutely necessary to fulfill the mitzva of shema and of kabbalat malkhut shamayim.
A similar situation unfolds in Berakhot (16a), which demands that the first section of shema be recited while desisting from work. Even omanim (workers) must pause their labor and recite the first section of shema; they may continue the remainder of shema while returning to their labor. Again, the gemara does not cite any source for this requirement. Once again, Tosafot claim that work stoppage is necessary to insure proper KAVANA. Tosafot refused to view the halakhot emanating from these gemarot as independent; both the demand for stationary recital (13b) and the requirement of work stoppage (16a) are intended to ensure proper kavana.
The problem with the view is that the SCOPE of these halakhot does not match the scope of the kavana requirement. The gemara previously ruled (Berakhot 13b) that kavana is only necessary for the first pasuk of shema; although the remaining sections of shema should ideally be recited with focus, kavana is not me'akev and the mitzva has been fulfilled even without proper kavana. If, minimally, kavana is only necessary during the first pasuk, why does the gemara (13b) require stationary recital beyond the first pasuk (either for the entire first chapter or for the first three pesukim)? Similarly, why does the gemara (16a)require cessation of work for the entire FIRST PARAGRAPH? If these two halakhot are merely facilitators of kavana, they should only be binding during the recital of the first pasuk, when kavana is absolutely necessary.
Tosafot in each gemara senses this problem and corrects the discrepancy. Although each gemara SUGGESTS different ranges for stationary shema and for shema while pursuing from labor, the halakha only DEMANDS these conditions for the first pasuk, the one which absolutely requires kavana. These gemarot are citing variant opinions which may have determined that additional texts, beyond the first pasuk, required kavana, and as such also require stationary recital and recital unencumbered by labor. However, since the gemara in Berakhot (13b) concludes that only the first pasuk requires kavana, these kavana conditions are only necessary during that pasuk. Effectively Tosafot maintain the logic that these extra requirements are merely kavana facilitators. Ultimately they are only necessary during the first pasuk which requires kavana. The expanded scope of these gemarot reflected positions which are not halakhically accepted.
The problem with Tosafot's solution is that Rava ruled that only the first pasuk requires kavana, yet he cites the opinion (16a) that the entire first chapter requires cessation of labor!
A different solution is suggested by the Maharitz Chiyut (cited by the Rashba (13b). Fundamentally, the stationary requirement and the demand to cease from labor ensure proper kavana. However, practically they must be implemented even for texts which dont require kavana. If a person were to be permitted to walk immediately after the first pasuk, the rendering of the first pasuk itself would be rushed and unfocused. By demanding that a person recite three pesukim while stationary, or even the entire first section, the halakha assures that the first pasuk itself will be recited calmly and serenely. Similarly, if a person is allowed to begin working too soon, the fist pasuk would just be a quick afterthought, hurriedly recited before returning to work. By delaying the return to work until after the first parsha, kavana during the first pasuk is ensured. Accordingly, these halakhot DO NOT represent a new requirement for shema but rather tactics and devices that enable and ensure proper kavana for the first pasuk.
Rabbenu Yona (in his comments on Berakhot 16a) claims that these halakhot DO represent an entirely new feature of shema. He cites a gemara in Yoma (19b) which prohibits even non-verbal signaling and body language during shema (eye-winking, lip movement, etc.). Involvement in this communication during shema renders the shema "arai" (literally, "temporary" or too "casual") since the shema is not being recited "alone," without concurrent activity. Similarly, labor performed during shema recital would compromise the stability of shema and convert it to arai. Independent of the kavana requirement, shema must be recited as keva and not arai. In fact the gemara in Yoma appears to derive this from the pasuk of ve-dibarta bam which is interpreted as a mandate to render shema recital as keva (focused) and not aria (casual). Since these requirements are independent of kavana, their range extends beyond the first pasuk; although kavana is only necessary for the first pasuk, keriyat keva may be necessary for larger swaths of shema.
Interestingly, Rabbenu Yona does not associate the stationary requirement with this new halakha of keriyat keva. Labor and bodily communication may subvert that single-mindedness of shema, but walking does not.
The Rosh, however, cites the Ra'avad, who in turn cites one of the Geonim, who claims that the keva requirement DOES prohibit walking during shema. Movement alone would render the shema arai.
To summarize, both Rabbenu Yona and the Geon cited by the Rosh acknowledge a new halakha of keva which governs shema. The Rabbenu Yona invalidates body signaling and labor because of this requirement while the Geon invalidates walking as well. Perhaps the differences between this view and that of Rabbenu Yona as to the scope of this new halakha of keva reflect different understandings of the halakha. The gemara in Yoma (19b) derives this "new" halakha from the words "ve-dibarta bam" render this recital keva and not arai. How does arai affect shema? Perhaps alternate activity dilutes the integrity of the recital. A recital is formal and declarative; alternative activities performed during the recital undermine the very recital. It is as if the shema were not formally recited, even though its text was verbalized and spoken. Based on this definition, other ACTIVITES, such as labor or even non-verbal communication, should be banned, as these activities can weaken the act of recital. However, since walking is a natural and thoughtless process, reciting shema during walking is no less formal or less declarative than stationary recital. Thus, Rabbenu Yona claimed that keva requires cessation of labor and avoidance of body signaling, but not stationary recital.
The Gaon cited by the Ra'avad, in contrast, may have understood the keva halakha differently. Shema must be a focused and concerted event, expressed not only by mental focus but by complete and exclusive physical investment. Everything else must be halted so that shema can be recited comprehensively and completely. Although walking would not compromise the ACT of recital and would not diminish its formality, it would lessen the comprehensive nature of shema. Therefore, not only does the arai concern ban labor or body language, but also movement.
In other words, Rabbenu Yona say arai is a halakha which bans activities which threaten to disrupt the actual recital (body signaling, labor). In contrast, the Gaon was not worried about the weakening effects of arai but was rather interested in a uni-focused recital of shema. Standing in place as opposed to walking is necessary to generate this posture and comprehensiveness.