The proof that Israel had no righteousness before God is followed on the positive side by an expansion of the main law laid down in Deu 6:4., to love God with all the heart, which is introduced by the words, “and now Israel,” sc., now that thou hast everything without desert or worthiness, purely from forgiving grace. “What doth the Lord thy God require of thee?” Nothing further than that thou fearest Him, “to walk in all His ways, and to love Him, and to serve Him with all the heart and all the soul.” אִם כִּי, unless, or except that, presupposes a negative clause (cf. Gen 39:9), which is implied here in the previous question, or else to be supplied as the answer. The demand for fear, love, and reverence towards the Lord, is no doubt very hard for the natural man to fulfil, and all the harder the deeper it goes into the heart; but after such manifestations of the love and grace of God, it only follows as a matter of course. “Fear, love, and obedience would naturally have taken root of themselves within the heart, if man had not corrupted his own heart.” Love, which is the only thing demanded in Deu 6:5, is here preceded by fear, which is the only thing mentioned in Deu 5:26 and Deu 6:24.
(Note: The fear of God is to be united with the love of God; for love without fear makes men remiss, and fear without love makes them servile and desperate (J. Gerhard).)
The fear of the Lord, which springs from the knowledge of one's own unholiness in the presence of the holy God, ought to form the one leading emotion in the heart prompting to walk in all the ways of the Lord, and to maintain morality of conduct in its strictest form. This fear, which first enables us to comprehend the mercy of God, awakens love, the fruit of which is manifested in serving God with all the heart and all the soul (see Deu 6:5). “For thy good,” as in Deu 5:30 and Deu 6:24.