Do you want an answer? I can't tell. It just seems like you are bitching about it in general.
The old testament represented one covenant. As a matter of fact, it foretold of Jesus and how that would change things. They weren't in opposition to one another. As a matter of fact, there's a bunch stuff that is really great teaching in the old testament. Just like lots of books that you read. It doesn't mean that you have to either accept all or none. Do you do that to all books that you read that were meant to help?
The old testament is absolutely 100% necessary to tell the story and see how we got to where we are. It shows the entire story of redemption and reconciliation to God. Let's not confuse what the bible is for here. For some, it is a place to place their anger for their own life struggles to unanswered questions. I'm over that. If you don't need redeemed then just walk on by. You don't need it, so reject it. If you do without a shadow of a doubt then why ever worry about it? I don't struggle with anorexia so I never think about it.
I really don't know why it is so hard to understand. One book is a book of laws. Those laws pointed to the depravity of man and a need for a saviour. The other book was a book of grace. It unfolded the plan for redemption. The new testament and the arrival of Jesus made it unnecessary to earn your own justification and longer. Thankfully it was done once and for all. At that point the ceremonies, rituals, laws and covenants were no longer needed for justification. So the ultimate obedience cancelled out the need for our effort to be justified. Instead of being hostile over it, it would seen that being thankful for it makes more sense, but that is just me.