It is really a new commandment. Recall that in the time of Moses, they were operating with the rule of an eye for an eye. Even our Lord Jesus noticed that slavery was the order of the day, there were classes with those on top lording it over the others.

The rule Jesus is giving them will change all these. It will change "an eye for an eye" to "when they hit you on one cheek turn the other". It will also change the rule of master-servant relationship, you now have to serve to be called a leader. What a rule! What a change! A 360 degrees change.

He says "love your enemies". How can they love their enemies when they dont even love those who are not their enemies. It is a terrific rule and a brand new one.

Disbelief is the feeling of not being able to believe.  They people did not believe in what Jesus was saying or doing because they believe that nothing can come out of the house of a poor man, knowing where he came from. But they forgot that God has rested his powers upon him to speak with authority