The Greatest Commandment

Once, a Gentile desiring to become a Jew, asked one called Shammai how to do so, but was harshly dismissed. He then asked Hillel and said if you can convince me while I stand on one foot, I will believe. Hillel said: "What is hateful to you, do not do to your fellow: this is the whole Law; the rest is commentary; go and learn" (Shab. 31a).

Hillel was probably thinking of the passage from Leviticus 19:18, but we may more easily recognize this as a teaching of Jesus from Mark 12:28-29 which includes Deuteronomy 6:5:

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.' The second is this: 'Love your neighbor as yourself.' There is no commandment greater than these." - NIV

All of the law of the Old Testament and teachings of the New Testament hangs on these simple yet profound ideas.