The belief in only one God is the most basic aspect of Judaism. As expressed in Deuteronomy 6:4-6, the shema. The first four of the Ten Commandments clarify how Israel was to worship God (worship God alone, without a graven image, without using his name in vain, by honoring the Sabbath). The first four of the Ten Commandments clarify how Israel was to worship God (worship God alone, without a graven image, without using his name in vain, by honoring the Sabbath).
The Shema was fundamental to daily practice of Jewish. The word refers to Deut. 6:4-5 (which begins “Hear O Israel,” shema is Hebrew for “Hear.”) The passage directs Jews to keep the commandments upon their heart and to teach them to their children. These commands are the Ten Commandments which immediately precede this command, but essentially the whole law is to be kept in mind and taught to the next generation.
Tamid 5.1 The superintendent said to them, “Say one blessing.” They said a blessing, pronounced the Ten Commandments, the Shema [Hear O Israel (Dt. 6:4–9)], “And it shall come to pass if you shall hearken” (Dt. 11:13–(21), and “And the Lord spoke to Moses” (Num. 15:37–41). They blessed the people with three blessings: True and sure, Abodah, and the blessing of priests. And on the Sabbath they add a blessing for the outgoing priestly watch. (Translation, Neusner)
Although the practice of reciting the shema is well-known in rabbinic sources, it is not possible to date those sources earlier than the second century. Avery-Peck, for example, suggests “there is no reason to posit a long history of legislation concerning its recitation” (Alan J. Avery-Peck, “Oral Tradition: Early Judaism,” ABD 5:35). Tan, on the other hand, argues the practice of reciting the shema dates to the pre-A.D. 70 period on the basis of b.Berakhot 21a.
However, there are several indications in the New Testament that the shema was used as a prayer even in the first century. Jesus alludes to the shema in Matt 22:34–40//Mark 12:28–34, Paul alludes to the 1 Corinthians 8:4, “there is no God but one” (See Erik Waaler) and James 2:19 appear to quote the shema. This is not evidence of twice-daily prayers, but the prayer was familiar neough to appear in three diverse contexts in the New Testament,
According to Berakhot 1.1-3. The shema was placed in doorways (the modern mezuzot) and in tephillin, boxes strapped to the hand and forehead during prayer. We know the tephillin were used in the first century since the pharisaical practice of making wide straps is criticized in Matthew 23:5. Aristeas 158 refers to the “words” posted on gates and doors and Josephus refers to the practice of binding scripture on the arm (Antiq. 4.213).
At the very least, the evidence suggests Jewish people in the Second Temple period recited the shema regularly and were ultimately committed to the idea of one God. There are obviously ramifications of this belief (rejection of other gods, for example). But there are other implications as early Jewish Christians described Jesus as divine (Phil 2:5-11, for example). How did Second Temple Jewish believers integrate their new believing Jesus into their understanding of “one God”?
Bibliography: Kim Huat Tan, “Jesus and the Shema,” pages 2677-2707 in Handbook for the Study of the Historical Jesus (ed. Tom Holmén and Stanley E. Porter; Leiden: Brill, 2011); “The Shema and Early Christianity,” Tyndale Bulletin 59 (2008): 181-206. Erik Waaler, The Shema and the First Commandment in First Corinthians: An Intertextual Approach to Paul’s Re-reading of Deuteronomy. WUNT 2/253. Tübingen: Mohr Siebeck, 2008).