In my last post, we continued the story in The Sign of Immanuel ~ Part 2 in Yesha’yahu 7:7-12. We learned that Achaz had put his fate in an alliance with Assyria rather than in God. In this post, we conclude our exploration of The Sign of Immanuel ~ Part 3 in Yesha’yahu 7:13-25.
17 Adonai will bring the king of Ashur [Assyria] on you, your people and your father’s house. These will be days worse than any you’ve known since Efrayim broke loose from Y’hudah.”
The Neo-Assyrian Empire was inaugurated soon after Tiglath-Pileser III’s accession to the throne in 745 BCE and was not to be overthrown until 612 BCE when Nineveh fell to the alliance of the Medes and Babylonians. At its height, it included all or part of the modern countries of Iran, Iraq, Turkey, Syria, Lebanon, Jordan, Isra’el and Egypt. Ashur’s reputation as an aggressive regime is supported by extensive documentation and stands as its historical legacy. Its strategy of psychological warfare included terrifying rhetoric, brutal destructions and carefully chosen examples of cruel torture. Its expansion was fueled by the potential for economic gain, which would come through the plunder, tribute, and tariffs that would result from control of trade and the trade routes
But it was not just Aram and the northern kingdom of Isra’el that would experience Assyrian devastation. Y’hudah would also suffer God’s punishment. As later events showed, paying Tiglath-Pileser III to take care of Achaz’s northern problem was not the smartest strategy. From that point on Achaz paid a heavy tribute as Ashur’s vassal.
18 Yes, when that day comes, Adonai will whistle for the fly in the farthest streams of the Nile in Egypt and for the bee in the land of Ashur.
Part of the lore of beekeeping maintained that a swarm could be lured out of its hive to another location by a whistling sound. Attacking armies are compared to flies and bees in Homer’s Iliad as well. 
19 They will come and settle, all of them, in steep vadis and holes in the rocks and on all thorn bushes and brambles.
This verse continues the imagery of bees by listing the places where bees are naturally inclined to make their hives. Such locations were also places of refuge for the desperate. However, Y’hudah’s enemies would find them there.
20 When that day comes, Adonai will shave – with a razor hired beyond the [Euphrates] River, that is, with the king of Ashur – the head and the hair between the legs and get rid of the beard as well.
While many translations suggest the shaving of the entire head, the forehead seems to be indicated explicitly by the Hebrew word. In Mesopotamia shaving off half the hair was used as a punishment intended to bring public humiliation. Additionally, a style of the haircut was used to designate a slave. Most commentators believe that the hair between the legs is a euphemism for pubic hair. 
21 When that day comes, a man will raise a young cow and two sheep. 22 Will they produce in abundance? No, he will [have to] eat curdled milk. Indeed, everyone left in the land will eat curdled milk and [wild] honey. 23 When that day comes, wherever there once were a thousand grapevines, worth a thousand pieces of silver, there will be only briars and thorns.
It is difficult to determine whether the text refers to a thousand vines that would be bought or sold for a shekel each (an exorbitant price), or, more reasonably, to a vineyard housing a thousand vines whose annual produce would bring a thousand shekels. The latter understanding would find support in Song of Songs 8:11. In short, the farmers faced near total disaster.
24 One will go there [to hunt] with bow and arrow because all the land will be briars and thorns. 25 You won’t visit hills once worked with a hoe, for fear of the briars and thorns; it will be good only for pasturing cattle and being trampled down by sheep. ~ Isaiah 7:17-25 (CJB)
Cattle and flocks could be devastating to agricultural land. Their movements would trample the soil, and their grazing would defoliate it, eventually leading to massive erosion of the topsoil and depletion of water sources.
In my next blog, we learn about The Assyrian Invasion in Yesha’yahu 8:1-10.
 Bible Background Commentary – The IVP Bible Background Commentary – Old Testament.