The fifth trumpet is likened to a war between locusts and humans (9:1-12). The locusts describe demons, the followers of the devil; here he is called by names that mean destroyer. His army is described as travelling rapidly around the earth, inflicting damage everywhere. The targets of the demonic powers are all humans apart from believers (9:4).
What should we learn from the fifth trumpet? One is that the powers of darkness are under the control of God. He decides when they can be unleashed. A second lesson is that there are times when God lets this happen for the detriment of humanity. It is possible that we are living in such a time because we can see much taking place that indicates evil influences in the world. This was the case when the Book of Revelation was written. The church of Jesus was undergoing opposition and God sent his judgements on the world by not hindering the powers that hate the world.
The sixth trumpet (9:13-19) contains details similar to the fifth in that an army follows four angels who are released for a specific time in order to kill one third of mankind by various plagues. It may be that John is using one of the fears that dominated Roman thinking, which was that the Parthians from the other side of the Euphrates would invade the Empire and destroy it. Their soldiers were regarded as fierce and were a suitable illustration of an army that is far worse.
The soldiers of this army ride on horses that have the power to poison their victims (like scorpions). This looks like another description of the demonic army. Since they are not allowed to commence their activities until God allows, we have here another reminder that he is in control of all creatures, and can use those who oppose him in the outworking of his plans. But it is also a reminder that there is a spiritual conflict taking place. God is working to save his people; the powers of darkness are working to destroy sinners eternally.
What was the response of people to the judgements indicated by the six trumpets? John tells us that they refused to repent of their sinful actions and attitudes towards God or towards one another. Living under circumstances of divine judgement does not change the hearts of sinners. They remain opposed to God and his kingdom.
We are reminded here of a basic perspective to have. John’s readers were informed that in the world there are basically two groups of people. There are those who are saved and there are those who are not. As far as the enemy powers of the bottomless pit are concerned, (a) they persecute Christians and (b) they work to destroy eternally everyone else. This is an obvious reminder why we should tell the gospel to those who are opposed to Jesus.