§2083
Morals › … › Chapter One: You Shall Love the Lord Your God With All Your Heart, and With All Your Soul, and With All Your Mind
Jesus summed up man's duties toward God in this saying: "You shall love the Lord your God with all your heart, and with all your soul, and with all your mind." This immediately echoes the solemn call: "Hear, O Israel: the LORD our God is one LORD."
God has loved us first. The love of the One God is recalled in the first of the "ten words." the commandments then make explicit the response of love that man is called to give to his God.
Source: Catechism of the Catholic Church (Vatican.va)