isaiah 9:3 Thou hast multiplied the nation, and not increased the joy: they joy before thee according to the joy in harvest, and as men rejoice when they divide the spoil. - Free Bible Online

      3. multiplied . . . nation--primarily, the rapid increase of Israelites after the return from Babylon; more fully and exhaustively the rapid spread of Christianity at first.
      not increased the joy--By a slight change in the Hebrew, its (joy) is substituted by some for not, because "not increased the joy" seems opposite to what immediately follows, "the joy," &c. HENGSTENBERG, retains not thus: "Whose joy thou hadst not increased," (that is, hadst diminished). Others, "Hast thou not increased the joy?" The very difficulty of the reading, not, makes it less likely to be an interpolation. HORSLEY best explains it: The prophet sees in vision a shifting scene, comprehending at one glance the history of the ChristianChurch to remotest times--a land dark and thinly peopled--lit up by a sudden light--filled with new inhabitants--then struggling with difficulties, and again delivered by the utter and final overthrow of their enemies. The influx of Gentile converts (represented here by "Galilee of the Gentiles") soon was to be followed by the growth of corruption, and the final rise of Antichrist, who is to be destroyed, while God's people is delivered, as in the case of Gideon's victory over Midian, not by man's prowess, but by the special interposition of God.
      before thee--a phrase taken from sacrificial feasts; the tithe of harvest was eaten before God (De 12:7; 14:26).
      as men rejoice . . . divide . . . spoil--referring to the judgments on the enemies of the Lord and His people, which usually accompany revelations of His grace.

JFB.