John is in the Heavenly Throne Room seeing the future eschatological event when the Lamb opens the first four seals. He gives us a picture of four horsemen.
The first is on a white horse and refers to Jesus (late in Revelation he is also on a white horse - Rev.19). White is symbolic of righteousness, crowns, and victories by Christ. If this is true, then before the other horsemen ride, the white horse will ride and attempt to reach the nations with the Gospel. Chapter 7 tells us that he succeeds with the multitudes of those who have been redeemed.
The second rider is on a fiery red horse. This symbolizes bloodshed and those who be killed by the sword or other violent means.
The third rider is on a black horse. The black horse symbolizes famine as food supplies are cut off. People are willing to give "a day's wages for a quart of wheat or three quarts of barley."
The fourth rider is on a green horse. The green symbolizes death. With bloodshed and famine, death will dominate.
Sure makes one grateful to know the Lord Jesus and be one of the redeemed. To all who come to him in faith and repentance, he will give forgiveness and eternal life. "For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord" (Romans 6:23). "For by grace you have been saved through faith, and not of yourselves; it is the gift of God. not by works, lest anyone should boast" (Ephesians 2:8,9).