The fifth trumpet contains many images that would have been familiar to readers in the time of John. Darkness is the opposite of light. In the New Testament it would represent a philosophy that denies Jesus and the gospel (John 3:18-21). The abyss is a place in which God confines demons (Luke 8:30, 31). And the tail is a symbol of lying prophets (Isa. 9:15).
While many parts of this trumpet remain mysterious, the "plague" is a spiritual one that torments the followers of Satan but does not harm those who are sealed (Rev. 9:4-6). It leaves the wicked in suicidal anguish (verses 5, 6). The sun of God's Word is eclipsed but not destroyed (verses 2, 3). The symbolism fits well with the effects of secularization in our world today.
Secularization is a process by which people become less and less attached to religious organizations. Not atheists, secular people just don't make time for God and/or religion. Such secularization isn't all bad, however, as it often sets the stage for a deeper appreciation of human rights and religious liberty. The secular commitment to universal education also gives people the tools to search the Word of God for themselves. Bible societies, scientific progress, and archaeology are hard to imagine in a world without freedom of thought and faith. So the secularization of the Western world has had its positive points.
But secularization, of course, has also had a negative impact. Through the French and Russian revolutions it opened the way for Communism, which made the practice of faith extremely difficult in Communist countries. Secularization has also paved the way for the wrong kind of ecumenism. All other things being equal, Christian unity would be a good thing. But a certain type of ecumenism impoverishes faith and steals away certainty, implying, "Don't be a fanatic. It doesn't really matter what you believe!" Also secularization has led to unbridled materialism. Particularly if you believe there is no God, then life at its fullest is mainly about shopping and eating. People with such beliefs usually become obsessed with the things of this world.
Ultimately, secularization is a trend that God has used to judge oppressors and free up His people to serve Him without restraint. And the beauty of the fifth trumpet is that it does not harm those who know God. A bumper sticker I saw a while ago states the ultimate Christian response to secularization: "God is not dead--I talked to Him last night."
Lord, in a world that ignores You in its pursuit of possessions and pleasure, keep me focused on Your living presence.