And now, Israel, what doth the LORD thy God require of thee, but to fear the LORD thy God, to walk in all His ways, and to love Him, and to serve the LORD thy God with all thy heart and with all thy soul; to keep for thy good the commandments of the LORD, and His statutes, which I command thee this day?The Ramchal explains this verse in the introduction to his classic book, Path of the Just:
This is what Moses our Teacher, may Peace be upon him, teaches us in saying (Deuteronomy 10:12), "And now, Israel, what does the Lord your God ask of you, but that you fear the Lord your God to walk in all His ways, and to love Him and serve the Lord your God with all your heart and all your soul, to observe the mitzvoth of God and His statutes. .. " Herein have been included all of the features of perfection of Divine service that are appropriate in relation to the Holy One Blessed be He. They are: fear of God, walking in His ways, love, wholeheartedness, and observance of all of the mitzvoth.That's all we need to do. Let's go!
"Fear of God" denotes fear of the Majesty of the Blessed One, fearing Him as one would a great and mighty king, and being ashamed at one's every movement in consequence of His greatness, especially when speaking before Him in prayer or engaging in the study of His Torah.
"Walking in His ways" embodies the whole area of cultivation and correction of character traits. As our Sages of blessed memory have explained, "As He is merciful, be also merciful..." The essence of all this is that a person conform all of his traits and all the varieties of his actions to what is just and ethical. Our Sages of blessed memory have thus summarized the idea (Avoth 2.1): "All that is praiseworthy in its doer and brings praise to him from others;" that is, all that leads to the end of true good, namely, strengthening of Torah and furthering of brotherliness.
"Love" - that there be implanted in a person's heart a love for the Blessed One which will arouse his soul to do what is pleasing before Him, just as his heart is aroused to give pleasure to his father and mother. He will be grieved if he or others are lacking in this; he will be jealous for it and he will rejoice greatly in fulfilling aught of it. "Whole-heartedness" - that service before the Blessed One be characterized by purity of motive, that its end be His service alone and nothing else. Included in this is that one's heart be complete in Divine service, that his interests not be divided or his observance mechanical, but that his whole heart be devoted to it.
"Observance of all the mitzvoth," as the words imply, is observance of the whole body of mitzvoth with all of their fine points and conditions.