How do we tackle the argument that the OT seems to believe that the Mosaic covenant is eternal?

[Dale (evolutionary providentialist)]

@adamjedgar

If we fail to keep the Sabbath we cannot enter into Christs rest, its that simple.

This is simple too:

But even if we or an angel from heaven should preach to you a gospel contrary to the one we preached to you, let him be accursed.
Galatians 1:8