Jesus responded to a this question. "What is the greatest commandment?"
in Matthew 22:35-40 & Mark 12:28-34
One of them, an expert in the law, tested him with this question: “Teacher, which is the greatest commandment in the Law?”

Jesus replied: "Love the Lord your God with all your heart and with all your soul and with all your mind. This is the first and greatest commandment. And the second is like it: Love your neighbor as yourself. All the Law and the Prophets hang on these two commandments.” Matthew 22:35-40 NIV

One of the teachers of the law came and heard them debating. Noticing that Jesus had given them a good answer, he asked him, “Of all the commandments, which is the most important?" “The most important one,” answered Jesus, “is this: ‘Hear, O Israel: The Lord our God, the Lord is one.  Love the Lord your God with all your heart and with all your soul and with all your mind and with all your strength.' (Dueteronomy 6:4-5)  The second is this: ‘Love your neighbor as yourself.' (Leviticus 19:8) There is no commandment greater than these.”
Mark 12:28-31.