Torah Observant Christians are basing their belief on the very words of Yeshua (Jesus) himself. (Yeshua was the name on his birth certificate since the "J" sound is not introduced until the 15th century.)
In Matt. 5: 17 Yeshua says he did not come to abolish the law but to fulfill it. In verse 18 comes the hard part. For He says: "for I tell you the truth, not one jot or tittle (one jot or least stroke of the pen) will be removed from the law until there is an new heaven and a new earth; AND all things are fulfilled."
Question one: Is there a new heaven and earth? I think that happens in Rev. 21.
Question two: Are all things fulfilled? If so then there is no need for Messiah to return.
So, not one portion of the law has been removed, according to Jesus.
How do we rationalize this point? We use words like "abrogate" or "completed" instead of fulfill. So I went to the original greek and noted the word actually means "to make whole" So he did not come to abolish, he came to make it whole.
Next, I suggest that you find the very definition of sin in the New Testament. Here are a few examples:
1 John 3:4 Sin is a violation of the law.
Romans 3:31 Do we throw out the law....no we uphold it!
Romans 6:1-2 Should we therefore sin that grace abound? Heaven forbid!!! How can we who have died to sin still live in it?
Finally, Yeshua said "I and the father are one."
and then "If you love me you will obey my commands." In Rev, 12 he says who are his nation? Those who know the testimony of Messiah and obey the commands of GOD. Why not the testimony and the command of the Messiah? Because the father set his marriage covenant for us in the form of the Torah.
I am going to suggest a speaker named Jim Staley and his teaching "truth or tradition" as a good step to the honest info here. Do not listen to others who do not have the whole truth. Seek the truth even if it is foreign to what you have been taught. Test every spirit.... heck test this posting. show me what I have wrong....