The New Covenant is with Jesus, not with us as individuals. Since we are in Christ, we share in that covenant all its benefits and all its promises.
“15 Brethren, I speak in the manner of men: Though it is only a man’s covenant, yet if it is confirmed, no one annuls or adds to it. 16Now to Abraham and his Seed were the promises made. He does not say, “And to seeds,” as of many, but as of one, “And to your Seed,” who is Christ” (Galatians 3:15-16 NKJV).
Since the New Covenant is between Jesus and the Father, we are simply a beneficiary of the New Covenant. We enjoy all its benefits without having to work at keeping it. Jesus, our representative, has already fulfilled all the conditions on our behalf. And because His obedience is perfect and His work is perfectly finished, that guarantees the covenant blessings.
All we can do is believe. We can rest in the finished work of Jesus. We can’t add to, delete from, or break the covenant. It’s ours by grace through faith.