Verses 25 and 26 leave the theme of the cursing of the women for a more general desolation of Israel. War will come upon Israel, and her young men will die in war, and the war will destroy the city. The image of the gates in verse 26 is a standard reference that stands for the whole of the city.
Anthropological note: In the ancient city, there were various circles of city life. The outskirts of the city were where agriculture occurred, and were the residence of the common and the poor. Closer in to the city would be more commercial locations. Central to the city was the walled portion, or the most secure part of the city. Those who lived inside the gates were the most important. The gates therefore represent not simply any town, but a walled city, and therefore an important location, in this case, Jerusalem. Just as the gates can stand for the walls in literary allusion, so they also stand for the city itself because the walled portion was such an important definition of an important city type.
Literary analysis:Verse 25 and 26 do not appear to flow directly from verses 16-24 which precede them. In fact, they flow from the entire theme of the destruction of Israel that is the general theme of Isaiah’s message. It is the verses 16-24 that function as a specific example inside the larger theme, with verses 25 and 26 returning to that larger theme.