On the first day of the holiday of Shavuot, which begins Tuesday evening, the passage in the book of Exodus that includes the Decalogue will be read in synagogues. While in many communities it is customary for the congregation to stand when the Ten Commandments are declaimed, ancient and modern rabbis have objected to this practice. Gil Student explains why:
At one point, some Jews had a custom of reciting the Ten Commandments as part of their daily prayers. Sectarians claimed this indicated a preference for this particular passage and a rejection of others as originating from a human rather than a divine author. In Israel [and Babylonia] during the 3rd century . . . this practice was rejected [by the talmudic sages] because of their concern over this sectarian argument against the sanctity of the [entire] Torah. . . . .
Who were the sectarians who believed that the Ten Commandments came from God but not the rest of the Torah? The great historian [of ancient Judaism] Geza Vermes suggests that they were Jewish Gnostics. Another scholar suggested to me that they were Marcionites, an early Christian sect who rejected the Hebrew Bible. Even in later centuries, after the Jewish Gnostics and the Marcionites were merely a footnote in history, the prohibition [against standing] remained in effect.
The same rationale was applied by later rabbinic authorities to discourage the practice of standing for the reading of the Decalogue. Arguing that it is worthwhile to follow this ruling even after its polemical purpose has become moot, Student notes that it is not only a reaction to heresy but a way of underscoring the fundamental dictum that all the Torah’s verses are equally holy, even—to use the Talmud’s example—the obscure genealogies found in the book of Genesis.