Was it John who looked into the scroll in Revelation 6:1?
Revelation 6:1 NASB
 "Then I saw when the Lamb broke one of the seven seals, and I
heard one of the four living creatures saying as with a voice of
No it is not John, for John was already invited to participate in these prophetic scenes, ( read Rev. 4:1-2 below) so the voice ,"as of thunder "is inviting others to participate in the episodes of the four horse riders.
Revelation 4:1-2 (NASB)
Scene in Heaven
4 "After these things I looked, and behold, a door standing open in
heaven, and the first voice which I had heard, like the sound of a
trumpet speaking with me, said, “Come up here, and I will show you
what must take place after these things.” 2 Immediately I was [a]in
the Spirit; and behold, a throne was standing in heaven, and One
sitting on the throne."