“burned up,” The judgment of God is often referred to as a fire; so this may not be a literal fire, but instead be referring to the judgment of God.
“few people are left.” Isaiah 24 is about the Tribulation period that is described in the book of Revelation. According to Daniel 9:27, the Tribulation will last a “week,” which refers to a week of years, or seven years. Between the troubles on earth during that time, which will include both natural disasters and wars, the vast majority of people and animals on earth will be killed, which is why “few people are left” alive on earth. It is sometimes taught that no one survives the Tribulation and Armageddon, but that is not true; there will be survivors on earth, and they will be judged in the “Sheep and Goat Judgment” of Matthew 25:31-46 (see commentary on Matt. 25:32).
God says in a few different ways that not many people will survive the Tribulation. Here in Isaiah 24:6, He says it very literally. However, in Isaiah 24:13 He makes the point by comparing the few people who are left on earth with the few olives that are left in the tree after the olive tree is beaten, and also with the few stalks of grain that are left in a field for the gleaners after the grain crop is harvested. Also, in Isaiah 13:12, God says the people on earth will be scarcer than pure gold, and in Jeremiah 25:33, God says the bodies of the people who are killed will be all over the face of the earth. Jesus taught that if the Tribulation was not a short period then no one would be left alive (Matt. 24:22).
To best understand Isaiah, however, we have to take the statement that “very few are left” in comparison to how many there were alive when the trouble started. Matthew 25:31-32 says that after the Battle of Armageddon, when Jesus has conquered the earth and is sitting on his throne, “all the nations will be gathered before him.” Since there are more than seven billion people on earth now, “very few” left could easily be several million people or more.
[For more on the Great Tribulation and the destruction during that time, see commentary on Dan. 12:1.]