What do think Jesus was doing the night He was betrayed? The Law came through Moses, grace and truth through Jesus Christ. (John 1:7.)
The New Covenant is in the precious blood of Jesus, shed for the forgiveness of sins. (Matthew 26:26-28). Hebrews explains the New Covenant, why it is necessary and what it means. This summary from Bible Hub explains it well:
The cross is the most glorious reality in all of human history and nobody here is diminishing it for a single moment.
But we need to go directly to what God Himself said the New Covenant actually is. Because a asked you to define it and I will tell you that the most authoritative definition does not come from Hebrews or from Bible Hub summaries however helpful those may be. It comes from the prophet God specifically chose to announce the New Covenant centuries before it arrived.
God spoke through
Jeremiah and defined the New Covenant in His own words with complete precision:
Behold the days come saith the Lord that I will make a new covenant with the house of Israel and with the house of Judah. Not according to the covenant that I made with their fathers in the day that I took them by the hand to bring them out of the land of Egypt which my covenant they brake although I was an husband unto them saith the Lord. But this shall be the covenant that I will make with the house of Israel after those days saith the Lord I will put my law in their inward parts and write it in their hearts and will be their God and they shall be my people. (Jeremiah 31:31-33 KJV)
Read that carefully. God defined His own New Covenant. And what did He say it contains? The same law. Written not on external tablets of stone but on transformed hearts by the Holy Spirit. Same law. New location. New power. New motivation. But the same law.
God did not say I will make a new covenant and replace My law with something different.
He said I will put My law in their inward parts and write it in their hearts. The newness of the New Covenant is not in the contents. It is in the method of delivery. The law moves from stone to heart. From external obligation to internal desire. From impossible demand on unchanged human nature to natural expression of a heart
genuinely transformed by the Spirit of God.
And Ezekiel confirmed exactly what the Holy Spirit does in that transformed heart:
I will put my spirit within you and cause you to walk in my statutes and ye shall keep my judgments and do them.(Ezekiel 36:27 KJV)
The Holy Spirit causes you to walk in God's statutes and keep His judgments. The same statutes. The same judgments. Including the Sabbath. Including all ten commandments. The New Covenant does not abolish what was written on stone. It writes it deeper on a heart that now genuinely desires to walk in it.
Now on Hebrews 8 and why God established an imperfect first covenant. The writer of Hebrews is not saying the Ten Commandments were imperfect or that they needed to be replaced with different contents. He is saying the old covenant was imperfect in its ability to transform the human heart from within. External law applied to an unchanged sinful heart produces only condemnation because sinful people cannot keep it in their own strength. That is the imperfection. Not the law itself but the inability of external law alone to produce genuine inner transformation.
Jesus confirmed this Himself. The law is not the problem. The unchanged human heart is the problem. That is why He said:
Think not that I am come to destroy the law or the prophets. I am not come to destroy but to fulfil. (Matthew 5:17 NKJV)
Fulfil. Not replace. Not abolish. Fill to its fullest and deepest meaning. And then He went deeper into every commandment in the Sermon on the Mount showing that genuine obedience goes all the way into the heart and not just the outward action.
And on the very night He
established the New Covenant with His blood He said with complete clarity:
If ye love me keep my commandments. (John 14:15 KJV)
The same night. The same Jesus. The New Covenant in His blood and the command to keep His commandments in the same conversation. He never presented them as contradictory. He presented them as inseparable.
So the New Covenant is not the blood of Jesus instead of the commandments. The blood of Jesus is what makes it possible for transformed hearts to finally keep the commandments from genuine love rather than external compulsion. The blood covers our failures. The Spirit writes the law on our hearts. And the result is exactly what God promised through Jeremiah. A people who know Him, who love Him and who walk in His ways from the inside out.
That is the New Covenant. Defined by God Himself. Not by Bible Hub.