Do Christians believe that Jews must still follow the Mosaic law? Deuteronomy 13:1-4 states:


All this word which I command you, that shall ye observe to do; thou shalt not add thereto, nor diminish from it.

If there arise in the midst of thee a prophet, or a dreamer of dreams--and he give thee a sign or a wonder,

and the sign or the wonder come to pass, whereof he spoke unto thee--saying: 'Let us go after other gods, which thou hast not known, and let us serve them';

thou shalt not hearken unto the words of that prophet, or unto that dreamer of dreams; for the LORD your God putteth you to proof, to know whether ye do love the LORD your God with all your heart and with all your soul.



The above passage seems to state that one may not subtract commandments from the Law of Moses which the Jewish people were commanded to obey, and  seems to imply that a true prophet will not do so. Do Christians believe that Jews must still obey the Mosaic Law, and if not, how is that consistent with the above passage?
It's a fundamental belief of Christianity that the coming of Jesus fulfils the Old Testament law. In other words that the Law was only ever intended to be until the coming of Messiah. Jesus did not therefore abolish or diminish the law. His coming simply marked the end of its original intended purpose. Jesus says as much in Matthew chapter 5 verse 17.


  “Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them.


Because of this Christians believe that nobody should be following the Law, Jews or non-Jews. A better way is available to them, namely following Jesus.

There are a relatively small number of Christians who believe that a way of salvation is open to the Jews who continue to follow the law, instead of Jesus, but it is a minority.