After the Sadducees struck out, it was the Pharisees turn. (The simple difference between the two, is to think of them as opposing political parties of Jewish leadership, but both saw Jesus as a threat.)
Here Jesus gave the summary: love God and love others.
Neither was a new command. The first commandment had always been the first law, the Shema from Deuteronomy: 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 strength. These commandments that I give you today are to be on your hearts. Impress them on your children. Talk about them when you sit at home and when you walk along the road, when you lie down and when you get up. Tie them as symbols on your hands and bind them on your foreheads. Write them on the doorframes of your houses and on your gates.
The second one was all of the interpersonal commandments wrapped up with a bow: Love your neighbor as yourself.
There are 613 commandments in the Torah, and Jesus lumped them all into two. There was no disputing his summary, but for people who felt that their responsibility was to hold people accountable to a list that defined righteousness, it took away some of their ammunition.
“Love God and love others” seems rather subjective; who will be the judge? Hmmm…