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...