Revelation 6

Now I saw when the Lamb opened one of the seals; and I heard one of the four living creatures saying with a voice like thunder, “Come and see.” v.1

Read chapter 6
Now we read of the seals being opened that no one was worthy to open but the Lamb as we saw in the previous chapter.  The reason that there are theses scrolls sealed up is that the Lord wasn't allowing them to happen.  When the Lord would break the seal what was not allowed for so long is now allowed.   This make sense as the premillennial kingdom before this great tribulation.  In God's kingdom there will be peace, there wont be wars, plagues, hunger or death often, yet all these things will happen once more for a time during this tribulation when these seals are opened and allowed again. John sees different horses and riders as the first four seals are opened and how each horseman is given something to cause either battle, conflict, scarcity, or death.   The fifth seal though does not have a horse but what John sees when the seal is opened are all those that have been martyred during this tribulation time and they are given a white robe (so not disembodied souls) and told to wait a little longer.  Then the sixth seal John see cosmic disaster and men going in to hiding during this day of God's wrath.  
This book and prophesy we need to remember is for a future time still and hard to grasp if we don't understand the the kingdom and the reason for the tribulation.  Let us realize though when God doesn't allow something to happen it wont, but when He gives man free will to choose or not- calamity results.