Deuteronomy 6:4

Hear, O Israel,.... These are the words of Moses, stirring up the people to an attention to what he was about to say of this great and momentous article, the unity of God, to prevent their going into polytheism and idolatry. From one of the words here used, the Jews call this section Kiriathshema, which they oblige themselves to read twice a day, morning and evening n; the last letter of the first word in this verse, "Shema", meaning "hear", and the last letter of the last word in it, "Echad", meaning "one", are greater than ordinary; which seems designed to excite the attention to what is contained in this passage:

the Lord our God is one Lord; the doctrine of which is, that the Lord, who was the covenant God and Father of his people Israel, is but one Jehovah; he is Jehovah, the Being of beings, a self-existent Being, eternal and immutable; and he is but one in nature and essence; this appears from the perfection of his nature, his eternity, omnipotence, omnipresence, infinity, goodness, self-sufficiency, and perfection; for there can be but one eternal, one omnipotent, one omnipresent, one infinite, one that is originally and of himself good; one self, and all sufficient, and perfect Being; and which also may be concluded from his being the first cause of all things, which can be but one; and from his relations to his creatures, as their King, ruler, governor, and lawgiver. And for this purpose these words are cited in Mark 12:29 but then they no ways contradict the doctrine of a trinity of persons in the unity of the divine essence, the Father, Word, and Holy Spirit, which three are one; the one God, the one Jehovah, as here expressed; see 1 John 5:7 and so the ancient Jews understood this passage. In an ancient book of theirs it is said o Jehovah, Elohenu, Jehovah (i.e. Jehovah, our God, Jehovah); these are the three degrees with respect to this sublime mystery; "in the beginning God (Elohim) created the heavens and the earth"; and again p, Jehovah, Elohenu, Jehovah, they are one; the three forms (modes or things) which are one; and elsewhere q it is observed, there are two, and one is joined to them, and they are three; and when the three are one, he says to (or of) them, these are the two names which Israel heard, Jehovah, Jehovah, and Elohenu (our God) is joined unto them; and it is the seal of the ring of truth, and when they are joined they are one in one unity; which is illustrated by the three names the soul of man is called by, the soul, spirit, and breath; and elsewhere they say r the holy blessed God, and his Shechinah, are called one; see John 10:30.

n Mist. Beracot, c. 1. sect. 1, 2. o Zohar in Gen. fol. 1, 3. p Ib. in Exod. fol. 18. 3, 4. q Ib. in Numb. fol. 67. 3. r Tikkune Zohar, Correct. 47. fol. 86. 2.