Having been instructed in the Jewish Torah and Rabbinical concepts of Law, the disciples would have been surprised at many of Jesus' sayings, deeds, miracles/healings worked on the Sabbath etc. They needed to be reassured that their Master was a law-abiding Jew. Jesus' basic attitude towards the Jewish inheritance was fundamentally positive and sympathetic even though it included some criticisms of pharisaical behaviour that he considered harmful. The whole of the Old Testament had religious value for the Jewish/Palestinian Christians of the first century and should continue to be respected in the new era inaugurated by Jesus.
What Jesus abhorred was hypocrisy: teaching one thing and doing another. Jesus Himself was a free spirit who directly confronted and resolved life situations in His healings and parables. But He never took the law into His own hands - as evidenced by His attitude during the temptations in the desert. He further paid His dues to Caesar, according to the law. The spirit of the Law was far more important to Him than the minute prescriptions of ceremonial cleansings and ritual worship of Judean society. Eventually, He would lay down His life in faithful obedience to the Father.
Ethical demands such as the Decalogue (10 Commandments) and the command to love God and neighbour transcend religion and time. They remain "till heaven and earth pass away." With the psalmist we pray:
"I keep the Lord ever in my sight."