And it was told the house of David - That is, the royal family; or the king and princes; the government. Ahaz was the descendant and successor of David.
Syria is confederate with Ephraim - Ephraim was one of the tribes of Israel, and the kingdom of Israel was often called “Ephraim,” or the kingdom of Ephraim; in the same way as the tribes of Judah and Benjamin were called the kingdom of Judah. The phrase, ‘is confederate with,’ is in Hebrew ‘resteth on;’ see the margin. The meaning is, that Syria was “supported by” Ephraim, or was allied with Ephraim. The kingdom of Israel, or Ephraim, was situated “between” Syria and Jerusalem. Of course, the latter could not be attacked without marching through the former, and without their aid. In this sense it was that Syria, or the Arameans, relied or “rested” on Ephraim. Though Syria was by far the stronger power, yet it was not strong enough to attack Jerusalem had the kingdom of Israel been opposed to it.
And his heart - The heart of the king - of Ahaz.
Was moved as the trees of the wood - This is a very beautiful and striking image. It expresses universal trembling, consternation, and alarm, as the trees are moved “together” when the wind passes violently over them. A similar expression is found in Ovid - in “Canaces,” Epist. xi. ver. 76, 77.
Ut quatitur tepido fraxina virga noto
Sic mea vibrari pallentia membra videres.