Isaiah returns to the theme of the remnant of Israel, which is actually the name of his son Shear-Jashub, as mentioned earlier in chapter 7 of this work. They will no longer lean on Assyria but on the Lord, Yahweh, the true holy one of Israel. This remnant returning was a common theme during the Exile.
The story of King Ahaz (736-716 BCE) can be found in 2 Kings, chapter 16 and 2 Chronicles, chapter 28. However, there was no mention of the prophet Isaiah in any of the stories about King Ahaz. Here, Yahweh told Isaiah to go with his son, whose name Shear-Jashub meant a remnant shall remain. They were to meet King Ahaz at the end of the upper pool on the highway to Fuller’s Field. This seems odd. Why not go to his palace or the king’s home in Jerusalem? Fuller’s Field was west of the walls of Jerusalem, where apparently some kind of soap was made. There is something symbolic going on.