With Deu 6:4 the burden of the law commences, which is not a new law added to the ten commandments, but simply the development and unfolding of the covenant laws and rights enclosed as a germ in the decalogue, simply an exposition of the law, as had already been announced in Deu 1:5. The exposition commences with an explanation and enforcing of the first commandment. There are two things contained in it: (1) that Jehovah is the one absolute God; (2) that He requires love with all the heart, all the soul, and all the strength. “Jehovah our God is one Jehovah.”
(Note: On the majuscula ע and ד in שְׁמַע and אֶחָד, R. Bochin has this remark: “It is possible to confess one God with the mouth, although the heart is far from Him. For this reason ע and ד are majuscula, from which the tsere subscribed the word עֵד, 'a witness,' is formed, that every one may know, when he professes the unity of God, that his heart ought to be engaged, and free from every other thought, because God is a witness and knows all things” (J. H. Mich. Bibl. Hebr.).)
This does not mean Jehovah is one God, Jehovah alone (Abenezra), for in that case לְבַדֹּו יְהֹוָה would be used instead of אֶחָד יְהֹוָה; still less Jehovah our God, namely, Jehovah is one (J. H. Michaelis). אֶחָד יְהֹוָה together form the predicate of the sentence. The idea is not, Jehovah our God is one (the only) God, but “one (or the only) Jehovah:” not in this sense, however, that “He has not adopted one mode of revelation or appearance here and another there, but one mode only, viz., the revelation which Israel had received” (Schultz); for Jehovah never denotes merely a mode in which the true God is revealed or appears, but God as the absolute, unconditioned, or God according to the absolute independence and constancy of His actions. Hence what is predicated here of Jehovah (Jehovah one) does not relate to the unity of God, but simply states that it is to Him alone that the name Jehovah rightfully belongs, that He is the one absolute God, to whom no other Elohim can be compared. This is also the meaning of the same expression in Zec 14:9, where the words added, “and His name one,” can only signify that in the future Jehovah would be acknowledged as the one absolute God, as King over all the earth. This clause not merely precludes polytheism, but also syncretism, which reduces the one absolute God to a national deity, a Baal (Hos 2:18), and in fact every form of theism and deism, which creates for itself a supreme God according to philosophical abstractions and ideas. For Jehovah, although the absolute One, is not an abstract notion like “absolute being” or “the absolute idea,” but the absolutely living God, as He made Himself known in His deeds in Israel for the salvation of the whole world.
As the one God, therefore, Israel was to love Jehovah its God with all its heart, with all its soul, and with all its strength. The motive for this is to be found in the words “thy God,” in the fact that Jehovah was Israel's God, and had manifested Himself to it as one God. The demand “with all the heart” excludes all half-heartedness, all division of the heart in its love. The heart is mentioned first, as the seat of the emotions generally and of love in particular; then follows the soul (nephesh) as the centre of personality in man, to depict the love as pervading the entire self-consciousness; and to this is added, “with all the strength,” sc., of body and soul. Loving the Lord with all the heart and soul and strength is placed at the head, as the spiritual principle from which the observance of the commandments was to flow (see also Deu 11:1; Deu 30:6). It was in love that the fear of the Lord (Deu 10:12), hearkening to His commandments (Deu 11:13), and the observance of the whole law (Deu 11:22), were to be manifested; but love itself was to be shown by walking in all the ways of the Lord (Deu 11:22; Deu 19:9; Deu 30:16). Christ therefore calls the command to love God with all the heart “the first and great commandment,” and places on a par with this the commandment contained in Lev 19:8 to love one's neighbour as oneself, and then observes that on these two commandments hang all the law and the prophets (Mat 22:37-40; Mar 12:29-31; Luk 10:27).
(Note: In quoting this commandment, Matthew (Mat 22:37) has substituted δαίνοια, “thy mind,” for “thy strength,” as being of especial importance to spiritual love, whereas in the lxx the mind (διάνοια) is substituted for the heart. Mark (Mar 12:30) gives the triad of Deuteronomy (heart, soul, and strength); but he has inserted “mind” (διάνοια) before strength (ἰσχύς), whilst in Mar 12:33 the understanding (σύνεσις) is mentioned between the heart and the soul. Lastly, Luke has given the three ideas of the original passage quite correctly, but has added at the end, “and with all thy mind” (διάνοια). Although the term διάνοια (mind) originated with the Septuagint, not one of the Evangelists has adhered strictly to this version.)
Even the gospel knows no higher commandment than this. The distinction between the new covenant and the old consists simply in this, that the love of God which the gospel demands of its professors, is more intensive and cordial than that which the law of Moses demanded of the Israelites, according to the gradual unfolding of the love of God Himself, which was displayed in a much grander and more glorious form in the gift of His only begotten Son for our redemption, than in the redemption of Israel out of the bondage of Egypt.
But for the love of God to be of the right kind, the commandments of God must be laid to heart, and be the constant subject of thought and conversation. “Upon thine heart:” i.e., the commandments of God were to be an affair of the heart, and not merely of the memory (cf. Deu 11:18). They were to be enforced upon the children, talked of at home and by the way, in the evening on lying down and in the morning on rising up, i.e., everywhere and at all times; they were to be bound upon the hand for a sign, and worn as bands (frontlets) between the eyes (see at Exo 13:16). As these words are figurative, and denote an undeviating observance of the divine commands, so also the commandment which follows, viz., to write the words upon the door-posts of the house, and also upon the gates, are to be understood spiritually; and the literal fulfilment of such a command could only be a praiseworthy custom or well-pleasing to God when resorted to as the means of keeping the commandments of God constantly before the eye. The precept itself, however, presupposes the existence of this custom, which is not only met with in the Mahometan countries of the East at the present day (cf. A. Russell, Naturgesch. v. Aleppo, i. p. 36; Lane, Sitten u. Gebr. i. pp. 6, 13, ii. p. 71), but was also a common custom in ancient Egypt (cf. Wilkinson, Manners and Customs, vol. ii. p. 102).
(Note: The Jewish custom of the Medusah is nothing but a formal and outward observance founded upon this command. It consists in writing the words of Deu 6:4-9 and Deu 11:13-20 upon a piece of parchment, which is then placed upon the top of the doorway of houses and rooms, enclosed in a wooden box; this box they touch with the finger and then kiss the finger on going either out or in. S. Buxtorf, Synag. Jud. pp. 582ff.; and Bodenschatz. Kirchl. Verfassung der Juden, iv. pp. 19ff.)