Under

Christ was born subject to – under –  all the Old Covenant laws. This explains why He was circumcised on the eighth day, a sacrifice was offered in the Temple for Him according to the Law of Moss, why He observed all the Holy Days of the Old Covenant, and so on. Yet, at the same time, He brought the New Covenant. Therefore, His teachings often spoke in terms of the New Covenant.  This New Covenant would come into force after His fulfillment of all the Law of Moses and His death.

4 But when the set time had fully come, God sent his Son, born of a woman, born under the law, 5 to redeem those under the law, that we might receive adoption to sonship. Gal. 4:4-5, NIV

Note just a few examples, in the famous Sermon on the Mount discourse, how Christ showed the law was going to expand in meaning in the New Covenant and take on a spiritual meaning. The Old Covenant basically only covered outward transgressions. This is due to the fact that the human will, apart from the Spirit of God, can only keep the outward meaning of the law but cannot control thoughts perfectly. Jesus kept the Law both in its outward intent and in all matters of the heart. He fulfilled both Covenants flawlessly. He is the only perfect Man whose righteousness is given to us as a gift through faith.

Murder

21 “You have heard that it was said to the people long ago, ‘You shall not murder, and anyone who murders will be subject to judgment.’ 22 But I tell you that anyone who is angry with a brother or sister will be subject to judgment. Again, anyone who says to a brother or sister, ‘Raca,’is answerable to the court. And anyone who says, ‘You fool!’ will be in danger of the fire of hell. Matt. 5:21-22, NIV 

Adultery

27 “You have heard that it was said, ‘You shall not commit adultery.’28 But I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart. Matt. 5:27-28, NIV

Love for Enemies

43 “You have heard that it was said, ‘Love your neighbor and hate your enemy.’ 44 But I tell you, love your enemies and pray for those who persecute you, Matt. 5:43-44, NIV