The event in this chapter happens between the sixth and seventh trumpets. John has already seen so much, but God is nowhere close to being finished. John looks to see another mighty angel coming from heaven robed in a cloud with a rainbow above his head; his face was like the sun, and his legs were like fiery pillars.
(It's funny how we see drawings and cartoons of angels and the artists don't come close to what God's heavenly angels truly look like.) This angel plants his right foot on the sea and his left foot on the land and gives a loud shout like the roar of a lion. When he shouted, the voices of the seven thunders spoke. What are the seven thunders? Nobody knows for sure; it's believed by some to be the voice of God. Many times, in the Bible, God's voice is described as thunder. Now, what do you think when you hear thunder? Power, awesomeness, fear, awe...That's how God is...all four descriptions and then some.
When the seven thunders spoke, John was about to write when he hears a voice from heaven telling him to seal up what the seven thunders had written and do not write it. Why would God want what was said not to be revealed? Nobody knows except that God is allowed to have secrets of His own. I'm sure many scholars are trying to break the code and find out, but it will be in vain. If God wanted it to be revealed, He would have allowed John to write it. End of story.
The angel standing on the sea and land then raises his right hand to heaven and sore by him who lives forever and ever, who created the heavens and all that is in them, the earth and all that is in it, and the sea and all that is in it, and said, "There will be no more delay! But in the days when the seventh angel is about to sound his trumpet, the mystery of God will be accomplished just as he announced to his servants the prophets."
Nobody knows for sure how the trumpet judgments are going to go. We don't know if the judgments will happen within minutes, hours, days, weeks, or months within each other, but trust and believe that they will happen.
The voice that John heard from heaven spoke to him once more telling him to go take the scroll that lies open in the hand of the angel who is standing on the sea and on the land. John goes up to the angel and asked him to give him the scroll. The angels tell him to take it and eat it. It will turn his stomach sour, but in his mouth will be sweet like honey. John takes the scroll and eats it. Sure enough, it's sweet in his mouth like honey. But once he eats it, his stomach turns sour. John is then told that he must prophecy again about many peoples, nations, languages, and kings.
What does it mean by the scroll being sweet and sour? The Gospel of Jesus Christ is sweet to the believers, but very sour to those who choose to walk in open rebellion against God. Those who follow Jesus and love Him enjoy hearing and reading the Word. Those who are lukewarm or straight up against God won't like the message because it makes them feel sour. But the message of Christ must still be preached. No matter how uncomfortable non-followers are, Jesus will still be preached.