“Hear, O Israel: the Lord, our God, the Lord is One” (Deuteronomy 6:4).
Commentary 1: “The Lord,” Who at present is “our God” and not the God of the other nations, in the future will be “One God.” As it states, “For then I shall convert the nations to a pure speech, that they may all call upon the Name of God” (Zephaniah 3:9) and “On that day God shall be One and His Name shall be One” (Zechariah 14:9). (Rashi, ad loc., citing the Sifri).
Commentary 2: In the Torah scroll, two letters in this verse, the ayin of Shema (“Hear”) and the dalet of Echad (“One”) are written larger than the rest. Together, they form the word eid, meaning “witness.” Because of Israel’s survival for thousands of years exclusively in the service of this idea, we remain the living witness of its absolute truth. The two large letters constituting the word “witness” remind us of our mission among the nations as witnesses of the One God (Rabbi Elie Munk, The Call of the Torah, abridged, ad loc.; also cf. Abudraham, ad loc.)