Please quote anyone who has suggested that "the old covenants (plural!) are no more".
Please quote anyone who has suggested that "we should not study it" (the sacrificial system).
By the end of the first century, likely most of the Christians were non-Jewish. Paul's efforts to bring the gospel to the gentiles saw to that. The churches he established around the Mediterranean would have grown and multiplied, while the church in Jerusalem was scattered and Jerusalem itself, and most of the Jewish nation, were destroyed in or around 70 AD.
I haven't seen this anywhere in Scripture. Please provide a reference.
Perhaps you could explain what you mean, and provide references.