Hebrews 12:22 says that, “The blood of Jesus speaketh better things than the blood of Abel.”
To understand the verse is to understand what the blood of this two people spake.
Gen. 4:9-11 made us to know that when Cain killed his brother Abel, the blood of Abel from the ground cried to God for vengeance. So, the blood of Abel spake vengeance. But on the other hand, Luke 23:33-34 tells us that Jesus asked the Father for our forgiveness while on the cross.
The blood of Jesus spake forgiveness. This is were the difference lies.

And to Jesus who is THE MEDIATOR OF THE NEW TESTAMENT…

Why is he the mediator of the new testament? It is because he came in the new testament to bring forgiveness and redemption, not judgment or condemnation. He said in John 3:17 For God came NOT into the world (in the new testament) to condemn the world but that the world through him might be saved.

But for us to be saved, we have to not refuse him that spake. We must first receive him to receive his salvation. Think about it.

John 1:12 says, “But as many as receive him, to them gave he power to become the sons of God”