Yes, the Old Covenant is still in effect for the Jews. But it has been whittled down over the millennia to its essentials. There is no longer a priesthood or prophetic function - these were continued on in Christianity. This doesn’t mean that Jews have no mystical life or that their prayers are fruitless - only that the definitive nature of priest and prophet have been left behind. For Jews who find they are unable to participate in the promised material blessings from God of the Mosaic covenant, Christianity is the appropriate alternative.
The Mosaic covenant was of blood and everlasting, (as the 10 commandments were written on stone, not on perishable paper like the rest of the covenant). The Aaronic priesthood had its own covenant of salt, so it only lasted while the salt had its savor, that is, until the priests lost their righteousness. This happened with the slaughter of the innocents and the crucifixion of Christ. The Melchizedek priesthood replaced the Aaronic priesthood with a more perfect covenant based on the blood of Christ.
The Christian covenant (which is almost unknown since it is one of the mysteries) is more perfect in holiness and spirituality than the Mosaic covenant, as Christ’s blood is a more perfect sacrifice than that of animals. Christ came for those that needed a physician, not those who lived correctly according to the law of Moses and enjoyed its blessings. At the second coming of Christ the two religions will be joined together into a new unity of law and grace for the Kingdom of God on the physical earth.