If the old covenant failed was it gods fault or the peoples fault for trying to keep it on their own power?

the old covenant was fulfilled in christ. that's why christians receive salvation. because when christ fulfilled all of the old covenant laws the christians receive his righteousness.how?they receive his righteousness the same way a bride receives the wealth of her groom. the church is the bride of christ and under this new covenant relationship we (the church) receive the righteousness of christ.this is why marriage is so sacred in Christendom because of its symbolic value.