Why does the apostle “[weep] much”? Was he emotionally overwrought because his desire to see the scroll's contents was denied, or is there more to it? His weeping signifies something momentous taking place. John, probably in his 90s at this point, had already seen and experienced extraordinary things. Given the amount of time God had worked with him, he must have attained a level of spiritual maturity of the highest order. Yet, this faithful servant—not given to whimsy—sobbed over what was at stake. Something shook him to the core—something far beyond mere disappointment over not having a prophecy opened.
In Revelation 5:4, John gives the primary reason for his weeping, and the issue is one of worthiness. Isaiah describes a similar circumstance where the prophet also has a vision of the Lord sitting on His throne (Isaiah 6:1). Seraphim are praising God, and at the sight of all this, Isaiah becomes unglued (verses 2-5), painfully aware of his uncleanness. He knows that in his state he is not worthy to look upon the Lord of Hosts.
However, a seraph touches Isaiah's mouth with a coal, removing his iniquity and purging his sin (verses 6-7). Then the prophet hears the Eternal asking, “Whom shall I send, and who will go for Us?” Isaiah eagerly answers the call and receives his commission (verse 8). With cleansing, he was fit—worthy—for God to use him to take a message to Judah.
However, in John's vision, something like a call goes out, but nobody answers it. Even with the cleansing that God is willing to do for His people—as He did for Isaiah—nobody can be found who is worthy. John, looking forward in vision to the Day of the Lord, sees that no angel in heaven, no servant of God on earth, and no spirit under the earth can open the scroll.
The matter of worthiness, then, must go beyond the matter of sin, because heaven is filled with angels who have not sinned, yet they still are unworthy to take the scroll. Likewise, as with Isaiah, God can purge the sin of His servants, but something even above sinlessness is needed to be worthy to open the scroll of Revelation.
What, exactly, makes this scroll's worth so great? John's reaction to it indicates that he was not ignorant of what it was; instead, he felt the full weight of its significance and expressed great distress over the absolute need for it to be opened. The apostle greatly desired the scroll to be opened, suggesting he knew that it contained something of tremendous worth, in addition to including judgments like the other prophetic scrolls.