You have multiplied the nation; you have increased its joy; they rejoice before you as with joy at the harvest, as they are glad when they divide the spoil.
3. Thou hast multiplied. This passage is somewhat obscure, both in itself, and on account of the diversity of interpretations; for it appears to be absurd to say that the joy was not increased, seeing that he immediately afterwards adds, they rejoiced.
The first words of this chapter plainly refer to the close of the foregoing chapter, where every thing looked black and melancholy: Behold, trouble, and darkness, and dimness - very bad, yet not so bad but that to the upright there shall arise light in the darkness (Psa 112:4) and at evening time it shall be light, Zac 14:7.
Commenting on Isaiah 9:1-7
Thou hast multiplied the nation,.... With light, knowledge, honour, and glory, even Galilee of the nations before mentioned, the land of darkness, and of the shadow of death, where the people dwelt; on whom Christ, the light, shone in the ministration of his Gospel to them; whereby the number of believers in Christ were multiplied; and indeed, as he conversed, preached, and wrought his miracles...