Mark 12:28-31 (NIV):
[28] 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?”

[29] “The most important one,” answered Jesus, “is this: ‘Hear, O Israel: The Lord our God, the Lord is one. [30] Love the Lord your God with all your heart and with all your soul and with all your mind and with all your strength.’ [31] The second is this: ‘Love your neighbour as yourself.’ There is no commandment greater than these.”