The rest, here, are the rest of the ones who were not marked with a seal and who did not die. These, too, despite the expectation that judgment might lead to reformation, did not repent. It provides the basis for seeing that there is such a thing as retributive judgment in which the purpose is not to convert, but to condemn. And lest we think this unfair, the context provides with a picture of men who know that God exists, but refuse to worship Him, turning instead to idols of God's created order to whom they ascribe religious worship. Man's idols are his greatest crimes against God.
False worship is the ultimate expression of man's rebellion.
One of the consequences of these visions of seals and trumpets is the expectation of evil that this world can expect. In one sense, the progressive nature of these seals and trumpets would seem to indicate an increasing presence of evil and hostility in the world. The interpretation adopted here views the progress of the gospel seems to parallel increasing hostility.