The new covenant is for the forgiveness of sins as clearly described in Mt. 26: 27–28
It is a blood covenant, to the death of both Signatories, the believer and Jesus. It is a permanent oath of irrevocable authenticity. Jesus mediates the problems that God and man have with one another, and with his own blood, comes up with a solution acceptable to both parties. Jesus substitutes his death penalty (that he didn’t deserve) for our death penalty (that we do deserve)
Jehovah’s Witnesses teach that they can get you into God’s Kingdom with out it, by some other way. Jesus says no:
“But when the king came in to look at the guests, he saw there a man who had no wedding garment. 12 And he said to him, ‘Friend, how did you get in here without a wedding garment?’ And he was speechless. 13 Then the king said to the attendants, ‘Bind him hand and foot and cast him into the outer darkness. In that place there will be weeping and gnashing of teeth.’ - Mt 22: 11
And here:
“Verily, verily, I say unto you, He that entereth not by the door into the sheepfold, but climbeth up some other way, the same is a thief and a robber… Then said Jesus…. I am the door". - John 10