They wanted a summary, and they got it from the highest authority, the Lord Jesus Christ.
The Pharisees had more than 600 laws. They had also questions: Which laws are more important? Which laws are less important? Another question was also: What is the most important law?
An expert in he law, who should have actually known the answer, asked the Lord Jesus Christ the last question: WHAT IS THE MOST IMPORTANT LAW?
What does the Lord Jesus Christ do? His answer comes from the Bible; he is quoting from the Old Testament: Deuteronomy 6:5 and Leviticus 19:18.
Deuteronomy 6:5 “AND YOU SHALL LOVE THE LORD YOUR GOD WITH ALL YOUR [MIND AND] HEART, AND WITH YOUR ENTIRE BEING, AND WITH ALL YOUR MIGHT.” (The Amplified Bible)
Leviticus 19:18 “YOU SHALL NOT TAKE REVENGE OR BEAR ANY GRUDGE AGAINST THE SONS OF YOUR PEOPLE, BUT YOU SHALL LOVE YOUR NEIGHBOR AS YOURSELF. I AM THE LORD.” (The Amplified Bible)
We keep all the others by fulfilling these two commands. These two commands summarize the Ten Commandments and the other Old Testament moral laws.
We find the Ten Commandments in the book of Exodus, chapter 20:1-17.