It is obvious that for there to be a new convenat there must have been an old one. I explain a little about the old covenant: This was about offering sacrifices for sins through certain animals, and certainly these sacrifices were never enough, since they had to be done continuously. On the other hand, there was also a wall between God and man, which was created at the time of man to sin, and there was a high priest who was the person who used to approach to God.
Now, that covenant that we just explained was replaced by a new one, a better one, a perfect one, which allows us to approach God without any problem and makes us heirs of Him.
The author of the Hebrews speaks to us about it and says:
15 And for this cause he is the mediator of the new testament, that by means of death, for the redemption of the transgressions that were under the first testament, they which are called might receive the promise of eternal inheritance.
16 For where a testament is, there must also of necessity be the death of the testator.
Who is the mediator of a new covenant? Jesus Christ is that mediator, because through His sacrifice on the cross He broke down that wall that stood between us and God, being a perfect sacrifice ended with sin for once and all, and that is why the apostle Paul says:
55 O death, where is thy sting? O grave, where is thy victory?
56 The sting of death is sin; and the strength of sin is the law.
57 But thanks be to God, which giveth us the victory through our Lord Jesus Christ.
1 Corinthians 15:55-57
Jesus Christ through His death on the cross and resurrection gave us redemption, forming a new covenant and making us heirs of the grace and eternal salvation that comes from God.
We can ask together with the apostle: Where is your sting, oh death? Where, o grave, is your victory? We must give glory to God for this, because without us deserving it He defeated death and its sting, suffering to the death to give us salvation.
Brethren, we have the greatest privilege of this land: We are heirs of an eternal inheritance, which is not corrupted and which no one can steal from us.