Albert Barnes Commentary Isaiah 9:12

"the Syrians before, and the Philistines behind; and they shall devour Israel with open mouth. For all this his anger is not turned away, but his hand is stretched out still." — Isaiah 9:12 (ASV)

The Syrians (Isaiah 7:1). The Syrians had been the allies of the Israelites. But after the death of Rezin, it is probable that they joined the Assyrians and united with them in the invasion of Samaria. - Aben Ezra; Grotius. "Before." Hebrew ‘From the east.’ Syria was situated to the east of Samaria, and the meaning here is that they would pour in upon Samaria from that side.

And the Philistines. The Philistines occupied the country southwest of Samaria, lying along the shores of the Mediterranean. It is not particularly mentioned in the Scriptures that they invaded Samaria after this prediction of Isaiah, but such an event is by no means improbable. They were long unsubdued, were full of hostility to the Jewish people, and were many times engaged with them in wars and several times subdued them (Judges 13:0; Judges 14:0; 2 Chronicles 28:18). The name Palestine is derived from Philistine, although this people occupied but a small part of the country; see Reland’s Palestine, chapter 7.

Behind. That is, from the west—the region where they lived. The sacred writers speak as if looking toward the east, the rising sun, and they speak of the west as the region behind them; see the notes at Job 23:8-9.

And they shall devour. Hebrew, ‘They shall eat.’ This figure is taken from a ravenous beast and means that they would come up with raging desires and fierce impetuosity to destroy the nation.

With open mouth. Hebrew, ‘With the whole mouth.’ The metaphor is derived from raging and furious animals. Chaldee, ‘In every place.’

For all this. Notwithstanding all this.

His anger ... see the note at Isaiah 5:25.