The Shema's opening declaration, 'Hear, O Israel, the Lord is our God, the Lord is one' (Deuteronomy 6:4), carries a distinctive Masoretic scribal feature: the final letter of the first word, Shema, an ayin, and the final letter of the last word, echad, a dalet, are conventionally written enlarged in Torah scrolls. Read together, the two enlarged letters spell the Hebrew word eid, witness, a pattern classical commentary treats as no accident, holding that the enlargement visually reinforces the verse's function as Israel's central act of testimony to God's oneness each time it is recited.
Source critics generally attribute the core of Vaetchanan, including the Decalogue restatement and the Shema, to the Deuteronomic source, read as a distinct literary and theological voice from the Priestly and combined Yahwist-Elohist material in the earlier books, marked by its own characteristic vocabulary of love, choice and exclusive loyalty to a single God worshipped at a single sanctuary. Traditional Jewish liturgy embeds the Shema in the daily morning and evening prayers, so a verse first delivered here as part of Moses' farewell address became, independently of its narrative setting, one of the most frequently recited sentences in Jewish devotional life.