This new covenant is made from blood that has never been seen before.
Abel's blood spoke.
His blood cries out against his murderer, Cain. Moreover, his blood exerts power even after death, in that it prevents Cain from ever settling again to work the ground. Quote by David Carr
"Cain became a wanderer (Gen 4:12-22). This blood of Abel’s proves more powerful and influential in the human story than was Abel himself". David Carr
So in other words Abel's life was taken because of his faith in God, and he was murdered by his brother. His blood called out to God and then we see Cain is administered a punishment from the Lord.
Christ's blood was also shed because of His faith in God and yet His blood cries out forgiveness for those who killed him. Two bloods spoke with powerful voices, both killed because others were jealous of them and one spoke revenge, and the other spoke forgiveness. Was this possibly something that was made know about Jesus blood compared to Abel's? There has never been blood spilled on the earth before like this blood. Christ's blood was recently discovered, revealed at how powerful this blood spoke in a new covenant.
Jesus , the mediator of a new covenant,and to the sprinkled blood that speaks a better word than the blood of Abel". ESV. "new/neas".
3501 néos – new ("new on the scene"); recently revealed or "what was not there before" including what is recently discovered.
3501 /néos ("new on the scene") suggests something "new in time" – in contrast to its near-synonym (2537 /kainós, "new in quality").
b. as respects substance; of a new kind; unprecedented, novel, uncommon, unheard of
All things are new, previously non-existent, begin to be far different from what they were before, high grade; superiority; excellence:
Hebrews 9:15 seems to focus on the transgressions that were made under the first covenant. This new covenant, by Christ's death, redeems those those that are called, so they can receive their inheritance.
Because of this, of a new covenant he is mediator, that, death having come, for redemption of the transgressions under the first covenant, those called may receive the promise of the age-during inheritance, Heb. 9:15
2537 kainós – properly, new in quality (innovation), fresh in development or opportunity – because "not found exactly like this before."
New, which as recently made is superior to what it succeeds.
Moses was the mediator of the old covenant but the One who is more than Moses inaugurates a fresh covenant which cannot fail as the former because it is founded on God's faithfulness alone. "The Mediator of a fresh covenant". Concordant commentary
The distinction in these two passages where the new covenant is used could be that one deals with a guarantee to an inheritance to those who are called. The second one should bring comfort to those who are relying on Christ's blood that sealed the covenant that has brought them to God.
2But, ye came to Mount Zion, and to a city of the living God, to the heavenly Jerusalem, and to myriads of messengers, 23to the company and assembly of the first-born in heaven enrolled, and to God the judge of all, and to spirits of righteous men made perfect, 24and to a mediator of a new covenant — Jesus, and to blood of sprinkling, speaking better things than that of Able.