Whatever it was that he saw, it was not a gentle occasion.

It makes sense in a distantly understandable way.

In the earliest years among the Abrahamic tribes, if you fell on hard times, you might lose your land and your family's livelihood.  The equivalent of modern bankruptcy, the legal process took title to your land and transferred it to a buyer.  You had the right to buy back your land, and the terms were recorded in a cover document that was attached to the deed, such as,  “Redemption requires payment of 10,000…” The deed and redemption document were rolled up and fastened with a seal of some sort.

Now if a relative of yours came to town and found you in bankruptcy, he might bail you out and restore your land by buying it back as described in the redemption document.  That kinsman would go to the keeper of records, probably at the temple, and make claim to the property by fulfilling the requirements.  The deed and redemption document could be unsealed if you or your kinsman came and claimed the land by paying the stated price.  Thus, the kinsman redeemer.

So later when the apostle John writes about seeing the sealed scroll, it makes a little more sense.  We can perhaps understand his weeping when no one could open the seals.  He saw the deed and redemption document for everything which mankind had lost, and it was all lost forever; and he wept.  

Then, this kinsman redeemer came to open the seals and pay the price for everything that had been taken from mankind so many years before.  In a practical, non-religious way, it does make sense.

The way John tells it … and you have to try visualize what he saw, all the way through ...

I saw a scroll in the right hand of the one seated on the throne. It was written on both sides and fastened with seven seals. I saw another who stood forward, calling out in a voice like thunder, "Is there anyone who can open the scroll, who can break its seals?” But there wasn't anyone able to break open the scroll and read it.

I wept in pain that no one was found to open the scroll, to break the seals.
I wept, until one of the elders said, “Don’t weep. Look - the lion from tribe Judah has conquered. He can open the scroll, he can break the seven seals.”

So I looked, and there was a lamb, slaughtered but standing tall. He came to the one seated on the throne and took the scroll from his right hand. In that moment, the four creatures and twenty-four elders bowed down and worshiped him. Each had an instrument and each had a gold bowl filled with incense, the prayers of holy people. Then with great voices, they sang:

Worthy! Take the scroll and open its seals.
Slain! Paying in blood, you bought men and women,
Bought them back from all over the earth,
Bought them back for God.
Then you made them a kingdom, priests for our God,
To rule the earth!

I looked again. I heard a company of angels around the throne, the creatures and the elders - ten thousand times ten thousand their number, thousand after thousand after thousand in great song:

The slain lamb is worthy!
Take the power, the wealth, the wisdom, the strength!
Take the honor, the glory, the blessing!

Then I heard every creature in heaven and earth and in underworld and sea, all joining in, all voices in all places, singing:

To the One on the Throne! To the Lamb!
The blessing,
The honor,
The glory,
The strength,
For age after age after age!

The four great creatures shouted out, “So It Is!” The elders fell to their knees and worshiped. 

So it is, in John’s describing of what he saw  ... everything that was lost is redeemed by the only one qualified, the only one who could pay the price.

That’s not so hard to grasp objectively, I guess. Huge, though. 

And as for what he actually saw ... we can hardly imagine. Whatever it was that he saw, it was not a gentle occasion.