Be still - The word used here - from רפה râphâh - means properly to cast down; to let fall; to let hang down; then, to be relaxed, slackened, especially the hands: It is also employed in the sense of not making an effort; not putting forth exertion; and then would express the idea of leaving matters with God, or of being without anxiety about the issue. Compare Exodus 14:13, “Stand still, and see the salvation of God.” In this place the word seems to be used as meaning that there was to be no anxiety; that there was to be a calm, confiding, trustful state of mind in view of the displays of the divine presence and power. The mind was to be calm, in view of the fact that God had interposed, and had shown that he was able to defend his people when surrounded by dangers. If this the divine interposition when Jerusalem was threatened by the armies of the Assyrians under Sennacherib, the force and beauty of the expression will be most clearly seen.
And know that I am God - See, in what I have done, the evidence that I am God. See a work accomplished which none “but” God could effect. Compare Isaiah 37:36.
I will be exalted among the heathen - That is, among the nations. The nations abroad that do not worship me, but worship idols, shall see in these deeds full proof that I am the true God, and that I am worthy of universal adoration. Compare the notes at Daniel 3:28-29; notes at Daniel 4:1-3, notes at Daniel 4:37. See also Exodus 9:16; Romans 9:17.
I will be exalted in the earth - In the lands abroad; all over the world. The defeat and destruction of the armies of Sennacherib were eminently suited to make a deep impression on the world that the God of the Hebrew people was the true God.