What did the blood of Abel cry out for... and what does the Blood of Christ speak that is better?

The answer is within the verse itself, there's nothing to figure out here. The blood of Christ speaks of the new covenant and better redemption than the shedding of blood through Abel. The "better" theme is found throughout the book of Hebrews. The sprinkling of blood shown here, by the way, is a powerful way to look at sprinkling in baptism, although I have no real argument with the death/burial/resurrection picture of immersion.