Let not your hearts faint, fear not. — In these words Isaiah strengthened Ahaz (Deuteronomy 7:4): “fear not, neither be faint-hearted.”
Tremble. — As in the Margin, “make haste.” (Comp. 2 Samuel 4:4, and 2 Kings 7:15.)
Be ye terrified. — A strong word. The idea is, “do not even be unnerved, much less alarmed, at the sight of them.”