Even when he [Jesus] appears to abrogate the Laws of Moses in some of the so called Antitheses of the sermon on the Mount, he does so in order to bring out what is, in his judgement, their true meaning and intent: The Law says do not murder, Jesus says not to be angry; the Law says not to commit adultery, Jesus says not to lust; the Law says take an eye for an eye, Jesus says turn the other cheek [Matt 5:21-48]. The deep intentions of these laws, for Jesus, are to be followed, not simply their surface meaning. Jesus saw the Law as a direction from God about how to live and worship.
Christians saw Jesus not as the founder of a new religion that cast aside the old, but as fulfilment of the old, who brought something new to an understanding of God that was already anticipated in the Hebrew bible.
 Ehrman, Lost Christianities, pg. 232  Ehrman, Lost Christianities, pg. 233