Actually, the whole understanding of scripture Old and New is more based on the Holy Spirit.  All the Apostles recognized what had been inspired by the Holy Spirit to be scripture and on the same level as all other scripture.  When Jesus speaks a rhema word to us it is still from Jesus and equal to all other revelation from Jesus.  The difference that we will have is our point of reference.  The Jews had the old testament but because of the rebellion of the Jews and the grace of God for the Gentiles, God blinded the hearts of the Jews so that even though they had the Old Testament that foretold of the Gospel of God through His son Jesus, they didn’t even recognize Jesus when He stood right in front of them.  The Jews were blinded for a reason and there will come a time when their blindness will be removed.  The Sabbath group, however, willfully blinded themselves to the Gospel taught in the New Testament.  Christ revealed many new things in the New Testament that can not be understood by containing it in the box of the Old Testament.  (Read the parable of the new and old wine skin)  These new things were a building towards where God is and moving away from where man was.  The OT was God taking Himself and putting Himself on man’s level.  Coming to dwell on earth and having man worship God in a physical way.  The NT is God moving things closer to where He is and having man worship in spirit and truth.  Remember Jesus saying that a time is coming and now is when man will neither worship here nor there but in spirit and truth.  Moving things to a spiritual level is why you really can eat anything.  Jesus himself says that nothing entering a man corrupts him but what comes out of the heart corrupts the man.  Now this teaching doesn’t blend with the OT thought because in the OT it was physical so God had purity on a physical level.  Now it is on a spiritual level.  Does that mean all of the OT is cancelled out? – no.  Does this mean Christians don’t obey the commandments of God – no way.  For God wrote His law on our hearts.  He tells us that.  The concept that is different is very much contained in the life of Paul.  He was a Jew, a very zealous Jew that killed the Christians because of the Law.  Did he finally come to the realization that the Christians were right and he was wrong by studying the law more?  No.  By studying the law more he persecuted the Christians even more.  It wasn’t until Jesus met him on the road to Damascus and revealed the new covenant to Paul that he was forever changed.  This new covenant is covered in Jeremiah 31 and again in Hebrews 8.  The new covenant comes into place because the Jews broke the old covenant and God turned away from them.  If the Sabbath group turns from the new covenant and places themselves back under the old covenant then you won’t be able to understand the mystery revealed in Jesus Christ.  Mainly because it just won’t fit.  What I saw in the old testament jews was pride, arrogance and anger when Jesus and the apostles tried to reason with them concerning the new covenant.  Ironically that is the same thing I saw in the Sabbath group…isn’t that incredible.