It is clear that the Four Horsemen of the Apocalypse—the first four seals—parallel Jesus' prophecy in Matthew 24:4-8, which ends with the words, "All these are the beginning of sorrows." Our Savior is letting us know that deception, violence, scarcity, and disease are only preludes to the catastrophic events of the last days. We could paraphrase His remark as, "These calamities are par for the course under man's civilization—far worse is yet to come."
The progression of disasters—of false ideas leading to war, war to famine, famine to pestilence, pestilence to wild beasts—is vital to understanding the spiritual teaching underlying the Four Horsemen. Through a kind of parable, Jesus is instructing us in the principle of cause and effect. If people believe the message of the father of murder (John 8:44) rather than the Prince of Peace (Isaiah 9:6), they will eventually turn to murder and war to resolve their differences. Like the law of gravity, war causes shortages of food, producing malnutrition and opening the door to disease.
God is showing us that these sorrows trace their roots back to disobedience and rejection of Him. Mankind has built his civilization on a foundation of sand (Matthew 7:24-27), and it is no wonder that disasters ensue upon mankind with terrifying regularity. Because God is just, it cannot be otherwise. He has said, "The wages of sin is death" (Romans 6:23), and "The soul who sins shall die" (Ezekiel 18:4). In addition, He has given us two sets of blessings and cursings (Leviticus 26 and Deuteronomy 28) to provide us frightening and vivid depictions of what happens when we disobey Him. The Four Horsemen are similar warnings or reminders that He is still on His throne, judging mankind for his sins.