The book sealed with seven seals, 1-8, which only the Lamb who was slain is worthy to open, 9-11. Therefore the elders praise him and confess that he redeemed them with his blood, 12-14.
1 And I saw in the right hand of him who sat on the throne a book written within and on the back, sealed with seven seals. 2 And I saw a strong angel proclaiming with a loud voice, "Who is worthy to open the book and to break its seals?" 3 And no man in heaven nor on earth, neither under the earth, was able to open the book, nor to look upon it. 4 And I wept much because no man was found worthy to open and to read the book, nor to look upon it. 5 And one of the elders says to me, "Do not weep. Behold, the Lion of the tribe of Judah, the Root of David, has prevailed to open the book and to break its seven seals."
6 And I beheld, and behold, in the midst of the throne and of the four living beings and in the midst of the elders stood a Lamb as though it had been slain, having seven horns and seven eyes, which are the seven Spirits of God sent forth into all the earth. 7 And he came and took the book out of the right hand of him who sat upon the throne. 8 And when he had taken the book, the four living beings and the twenty-four elders fell down before the Lamb, each of them having harps and golden vials full of odors, which are the prayers of saints. 9 And they sang a new song, saying, "You are worthy to take the book and to open its seals, for you were slain and have redeemed us for God by your blood out of every kindred, language, people, and nation, 10 And have made us kings and priests to our God. And we shall reign on the earth."
11 And I beheld, and I heard the voice of many angels around the throne, the living beings, and the elders. And their number was ten thousand times ten thousand, and thousands of thousands, 12 Saying with a loud voice, "Worthy is the Lamb who was slain to receive power, riches, wisdom, strength, honor, glory, and blessing." 13 And every creature which is in heaven, on the earth, under the earth, and those which are in the sea, and all which are in them, I heard saying, "Blessing, honor, glory, and power be to him who sits upon the throne and to the Lamb forever and ever." 14 And the four living beings said, "Amen." And the twenty-four elders fell down and worshiped him who lives forever and ever.
Matthew Henry Commentary - Revelation, Chapter 5[➚]
[v.6-10] - Reference, Genesis 9:4; Leviticus 17:11; Deuteronomy 12:23. Leviticus 17:11 states that, "the life of the flesh is in the blood," and that, "it is the blood that makes an atonement for the soul." It is only by the atoning blood of Christ that we may have the new life and eternal life. He purchased, or redeemed, His people by the shedding of His blood.
[v.9] - "and have redeemed us" - Reference, Acts 20:28; 1st Corinthians 6:20, 7:23; Titus 2:14; 1st Peter 1:18-19, 3:18.