In a sense, this is a restatement of the First Commandment -- and our response to the fact that God loves us and is our God. In other words, the love of God is our very first duty.
The love of God! Think of it! Not the knowledge of Torah, regardless of how edifying or noble; not external observances, regardless of how scrupulously or beautifully observed; not the practice of Jewish minhagim (customs), regardless of how much they might make us feel identified with God's Chosen People; not even the love of friends, as tender and warm as that may be. No. Yeshua's answer is that the greatest duty of our lives is to love God with every bit of our passion, inwardness, and strength...
When we walk in the power of the Holy Spirit and the fruit of the Holy Spirit is truly produced within us, we will not find ourselves walking contrary to the way of the Torah (Gal. 5:22-23), and the inward motivation of the Torah will be written upon our hearts
(Jer. 31:33). As Rav Sha'ul (Paul) wrote in Romans 13:10, "Love is the fulfilling of the law."