Albert Barnes Commentary Isaiah 28:18

"And your covenant with death shall be annulled, and your agreement with Sheol shall not stand; when the overflowing scourge shall pass through, then ye shall be trodden down by it." — Isaiah 28:18 (ASV)

And your covenant with death - (see the note at Isaiah 28:15).

Shall be disannulled - The word rendered ‘shall be disannulled,’ (וכפר v^ekupar from כפר kâphar), properly means “to cover, overlay;” then to pardon, forgive; then to make atonement, to expiate. It has the idea of blotting out, forgiving, and obliterating—because a writing in wax was obliterated or “covered” by passing the stylus over it. Hence, also, the idea of abolishing, or rendering void, which is the idea here. When the overflowing scourge (see the note at Isaiah 28:15).

Then you shall be trodden down by it - There is in this verse a great intermingling of metaphor, not less than three figures being employed to denote the calamity. There is first the scourge, an instrument of punishment; there is then the idea of inundating waters or floods; then there is also the idea of a warrior or an invading army that treads down an enemy. All the images are designed to denote essentially the same thing: that the judgments of God would come upon the land, and that nothing in which they had trusted would constitute a refuge.