The Catechism in Questions & Answers

284. What does the commandment to love God demand, and what does this require?

Love for God is to characterise a person’s being and define his conduct.
The commandment to love God applies to the person as a whole and requires his full effort: “And you shall love the Lord your God with all your heart, with all your soul, with all your mind, and with all your strength” (Mark 12: 30). This signifies undivided devotion to God.