(4) Hear, O Israel! The LORD is our God, the LORD alone. (5) You shall love the LORD your God with all your heart and with all your soul and with all your might. (6) Take to heart these instructions with which I charge you this day. (7) Impress them upon your children. Recite them when you stay at home and when you walk along the way, when you lie down and when you get up.
MISHNA: Beit Shammai and Beit Hillel disputed the proper way to recite Shema. Beit Shammai say: One should recite Shema in the manner indicated in the text of Shema itself. Therefore, in the evening every person must recline on his side and recite Shema, in fulfillment of the verse: “When you lie down,” and in the morning he must stand and recite Shema, in fulfillment of the verse: When you rise, as it is stated: “When you lie down, and when you rise.” And Beit Hillel say: Every person recites Shema as he is, and he may do so in whatever position is most comfortable for him, both day and night, as it is stated: “And when you walk along the way,” when one is neither standing nor reclining (Me’iri). If so, according to Beit Hillel, why was it stated: “When you lie down, and when you rise”? This is merely to denote time; at the time when people lie down and the time when people rise.
Rabbi Tarfon said: Once, I was coming on the road when I stopped and reclined to recite Shema in accordance with the statement of Beit Shammai.
The Sages said to him: You deserved to pay with your life, as you transgressed the statement of Beit Hillel.
ת"ר בה"א עומדין וקורין יושבין וקורין ומטין וקורין הולכין בדרך וקורין עושין במלאכתן וקורין
The Sages taught in a baraita that Beit Hillel say: One may recite Shema in any situation: Standing and reciting, sitting and reciting, reclining and reciting, walking and reciting and even working and reciting.
(א) קוֹרֵא אוֹתָהּ מְהַלֵּךְ, אוֹ עוֹמֵד, אוֹ שׁוֹכֵב, אוֹ רוֹכֵב עַל גַּבֵּי בְּהֵמָה, אוֹ יוֹשֵׁב, אֲבָל לֹא פְּרַקְדָּן, דְּהַיְנוּ שֶׁפָּנָיו טוּחוֹת בַּקַּרְקַע, אוֹ מֻשְׁלָךְ עַל גַּבּוֹ וּפָנָיו לְמַעְלָה, אֲבָל קוֹרֵא וְהוּא שׁוֹכֵב עַל צִדּוֹ: ..וְאִם הָיָה בַּעַל בָּשָׂר הַרְבֵּה, וְאֵינוֹ יָכוֹל לְהִתְהַפֵּךְ עַל צִדּוֹ, אוֹ שֶׁהָיָה חוֹלֶה, נוֹטֶה מְעַט לְצִדּוֹ וְקוֹרֵא.
The Shma may be recited walking, standing, lying down, riding on an animal, or sitting. It may not be recited while lying face down or face up, but rather lying on one's side.... If one is corpulent, and can't roll over on their side, or if one is sick, then they should slightly incline to their side and recite it.
Lawrence Hoffman, My People's Prayer Book, Vol. 1, 91-92.
Reform congregations say the Shma standing. Halacha prescribes sitting, not standing, for the Shma. The issue goes back to a debate between Beit Hillel and Beit Shammai, in which Beit Hillel ruled (successfully) that the Shma should be said in whatever position one happened to be when the time of its recitation arrived. In the ninth century, the Babylonian scholar, Amram Gaon, enforced that position, as part of his religio-political attack on the Palestinians who still said the Shema standing. His successful championing of the Hillelite perspective eventually entered the codes of Jewish law...When the Crusaders overran Palestine, destroying native Palestinian Jewish custom in the process, the Palestinian practice of standing died too, so that Jews round the world now sat for the Shma as Amram had insisted.
Reform Jews, however, saw the Shma as central to their claim that Judaism's uniqueness lay in its discovery of ethical monotheism. Wanting to acknowledge the centrality of the Shma, and recognizing that people generally stand for the prayers that matter most, they began standing for the Shma despite the Halacha. They justified their position by arguing that the halachic act of sitting for the "watchword of Jewish faith" was inconsistent with the halachic principle of aceepting the yolk of heaven: how could one not stand to proclaim God one?
R. Levi Cooper, Relics for the Present, 94.
[In the name of R. Shlomo Hayyim Friedman, Rebbe of Sadigura]
Beit Hillel is giving voice to the idea that Divinity permeates our entire world. In every place, at every moment, in every situation - whether we are lying down, standing still or walking - Godliness is present. Whatever the scenario, the Divine should be sought and the yoke of Heaven accepted...
Rabbi Tarfon mistakenly thought that accepting God's presence required a certain physical posture...in truth, God's presence permeates the world under all circumstances and without interruption...the Almighty is not confined to a particular location or position; indeed there is no place that is empty of the Divine Presence.
There are times and places in which connecting to that unlimited Presence may be easier - perhaps when praying with a congregation and using the very same words that have been on the lips of our people for generations...