In the previous chapter, Isaiah and a prophetically named son came to Ahaz with a sign. The sign was that a young woman would conceive a son who would not be very old before Assyria would come.
In this parallel prophecy, we have a second prophetically named son of Isaiah, Maher-shalal-hash-baz, or “making speed to the spoil; he hastens to the prey.” While Shearjashub was a hopeful “remnant will return,” this son foretells doom.
The writing of the name on a great roll, and it being witnessed by two faithful witnesses in accord with the law of witnesses, demonstrates the importance of the omen. Although presented as a son, the context here may or may not have referred to a physical child. Rather, as with Shearjashub, a woman who had not yet conceived would bear a child who would witness the destruction before they were very old. That the women had not yet conceived simply makes the timing indeterminate—but still soon.