And thou shalt love the LORD thy God with all thine heart, and with all thy soul, and with all thy might.

Wesley's Notes

6:5 And thou shalt love the Lord thy God with all thine heart - And is this only an external commandment? Can any then say, that the Sinai - covenant was merely external? With all thy heart - With an entire love. He is One; therefore our hearts must be united in his love. And the whole stream of our affections must run toward Him. O that this love of God may be shed abroad in our hearts.

Matthew Henry's Concise Commentary

6:4,5 Here is a brief summary of religion, containing the first principles of faith and obedience. Jehovah our God is the only living and true God; he only is God, and he is but One God. Let us not desire to have any other. The three-fold mention of the Divine names, and the plural number of the word translated God, seem plainly to intimate a Trinity of persons, even in this express declaration of the unity of the Godhead. Happy those who have this one Lord for their God. It is better to have one fountain than a thousand cisterns; one all-sufficient God than a thousand insufficient friends. This is the first and great commandment of God's law, that we love him; and that we do all parts of our duty to him from a principle of love; My son, give me thine heart. We are to love God with all our heart, and soul, and might. That is, 1. With a sincere love; not in word and tongue only, but inwardly in truth. 2. With a strong love. He that is our All, must have our all, and none but he. 3. With a superlative love; we must love God above any creature whatever, and love nothing but what we love for him. 4. With an intelligent love. To love him with all the heart, and with all the understanding, we must see good cause to love him. 5. With an entire love; he is ONE, our hearts must be united in his love. Oh that this love of God may be shed abroad in our hearts!