What does Hebrews 12:24 mean?

This verse completes a comparison between how God presented man with the old covenant, versus how He presents man with the new covenant. At Mount Sinai, the people of Israel were shown that God is absolutely holy and unapproachable by sinful man. This is why God used clouds, fire, trumpets, and so forth to inaugurate His covenant through Moses (Exodus 19:9–20). On the other hand, Christ offers us a new covenant, one which removes the barrier between men and God (Hebrews 9:24), and which allows us to approach the throne of God with confidence (Hebrews 4:16). As a result, we "come to" this new covenant in a tone of peace and rest, rather than one of fear and judgment. This scene is depicted to include celebration, angels, and the departed Christians who wait for us to join them.

Here, Christ is mentioned as the final component of that glorious scenario. Earlier in the book of Hebrews, it was mentioned that Christ's work in heaven was the "real" sacrifice which the blood offered in earthly temples was meant to symbolize (Hebrews 9:23–28). Once again, Jesus Christ is mentioned as the "mediator" of this new covenant. This is from the Greek term mesitē, which literally means someone who goes between two parties to resolve a dispute. In modern English, we might call this person an arbitrator. Christ, and Christ alone, serves to bridge the gap between sinful men and a perfectly holy God (1 Timothy 2:5–6).

Earlier in this letter, the writer mentioned Abel, whose untimely death did not prevent him from being counted as an example of godly faith (Hebrews 11:4). In that reference, it was said that Abel "still speaks," in spite of his death. Of course, Abel's blood was shed without his consent (Genesis 4:8), in an act that demanded retribution (Genesis 4:10). In contrast, Christ's blood was shed of His own will (John 10:17), and rescues mankind from the penalty of their own sins (Isaiah 53:5).