These practices derived in large part from contemporary interpretations of the biblical prohibition against "taking the name of YHWH your God in vain" (Ex. 20:7; Dt. 5:11). Based on the Jewish tendency to "make a hedge for the Law"—which is to say, interpret the Law in the broadest sense possible to prevent one from even coming close to breaking a commandment—Jews increasing refused to say God's name at all. The transformed nature of this prohibition is most clearly reflected in the Greek translation of Leviticus 24:11-16. The Hebrew text reads: "whoever blasphemes/slanders the name of YHWH shall surely be put to death" (Lev. 24:16). But the Greek Septuagint, reflecting Jewish beliefs and practices in the second century B.C., reads: "whoever names the name (onomazōn de to onoma) of the Lord (kurios)—by death let him be put to death." In other words an original prohibition against misusing the name YHWH was transformed by at least the second century B.C. into a prohibition against even pronouncing the name at all.
There were two exceptions to this general prohibition. The first, and most important, was the pronunciation of the name YHWH by the High Priest at the temple on the Day of Atonement. The biblical text of the Day of Atonement ritual in Leviticus 16 does not mention a specific benediction to be said in the name of YHWH. Our information on the ritual pronunciation of the Name on the Day of Atonement comes from the Mishnah, a collection of rabbinic oral traditions recorded around A.D. 200.
When the priest and the people which stood in the Temple Court [on the Day of Atonement] heard the Expressed Name [YHWH] come from the mouth of the High Priest, they used to kneel and bow themselves and fall down on their faces (Mishnah, Yoma 6.2, 3.8, 4.2).
The book of the Wisdom of Sirach contains a detailed description of the Day of Atonement ritual performed by the High Priest Simon II, the Just (219-196 B.C.) (Sirach 50), and also mentions the people prostrating themselves at the mention of the Name (Sirach 50:20-21), just as described in the Mishnah. The Talmud records a tradition that after the death of Simon, people ceased to speak the Name aloud.
The name of YHWH was also invoked during the daily recitation of the priestly benediction described in Numbers 6:22-27. When the priests pronounced this blessing, "in the Temple they pronounced the Name as it was written, but in the provinces by a substituted word [ha-šēm or ădōnāy]." The Talmud, a 4th to 6th century A.D. commentary on the Mishnah, describes this practice:
R. Tarfon said: "I once ascended the dais [of the temple] . . . and inclined my ear to the High Priest, and heard him swallowing [i.e., whispering or pronouncing indistinctly] the Name [YHWH] during the chanting by his brother priests." (Babylonian Talmud, Kiddushim 71a.)
If this report is accurate, it means that the name may have been whispered so that only nearby priests could hear it distinctly, but not the people receiving the blessing, thus not revealing the sacred name to the non-priests. When the temple was destroyed and the ritual pronunciation of the name ceased, priestly and rabbinic scholars preserved the correct pronunciation for several centuries by whispering the name to their disciples once every seven years, but eventually the correct pronunciation of the sacred name was lost.
The rabbis similarly creatively misread Exodus 3:15 as authorization for this practice. The text says that YHWH is to be God's name "forever," in Hebrew lĕ-ʿōlām. The unvoweled Hebrew word is L-ʿLM, which can voweled and read as as lĕ-'allēm (Lĕ-ʿaLLēM instead of Lĕ-ʿōLāM), which renders the meaning "concealed." Thus, they took this passage as a command to conceal rather than pronounce the divine name revealed by God to Moses. This is part of the rabbinic tradition of God's hidden, unpronounceable, and "ineffable name," the šēm ha-mĕfôrāš.
This phrase is not found explicitly in the Hebrew Bible, but derives from an Aramaic Targum interpretation of Judges 13:18, where an angel asks, in Hebrew, "Why do you ask my name, seeing it is wonderful (pelīʾy)?" The Aramaic Targum of Judges translates "wonderful" as mĕpāraš "ineffable," meaning that the name of God is unpronounceable or unknowable. By the era of Jesus there was thus a strong tradition of the sacred secrecy of God's name, which could only be revealed in the temple by the High Priest on the Day of Atonement or in temple blessings.
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