The word 'echad, "one," is used in the Jewish Scriptures in either a compound or absolute sense. In what sense is 'echad used in the Shema, "Hear, O Israel, the Lord our God, the Lord is One" (Deuteronomy 6:4)?
In such verses as Genesis 1:5: "And there was evening and there was morning, one day," and Genesis 2:24: "Therefore shall a man leave his father and his mother and shall cleave to his wife, and they shall be one flesh," the term 'echad, "one," refers to a compound united one. However, 'echad often also means an absolute one. This is illustrated by such verses as 2 Samuel 13:30: "Absolom has slain all the king's sons, and there is not one of them left"; 2 Samuel 17:12: "And of all the men that are with him we will not leave so much as one"; Exodus 9:7: "There did not die of the cattle of Israel even one"; 2 Samuel 17:22: "There lacked not one of them that was not gone over the Jordan"; Ecclesiastes 4:8: There is one [that is alone], and he has not a second; yea, he has neither son nor brother." Clearly, the word "one" used in these verses means an absolute one and is synonymous with the word yachid, "the only one," "alone." It is in this sense, with even greater refinement, that 'echad is used in Deuteronomy 6:4: "Hear, O Israel, the Lord our God, the Lord is One." Here, 'echad is used as a single, absolute, unqualified one. There is no mention of a triune god.