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.
Thou hast multiplied the nation - primarily, the rapid increase of Israelites after the return from Babylon: more fully the rapid spread of Christianity at first: ultimately and exhaustively the multiplication of Israel in the last days, when it shall be restored as a nation (Isaiah 66:8-10).
(And) not increased the joy. By a slight change in the Hebrew х low (H3807a)], its (joy) is substituted by the Qeri' for NOT х lo' (H3808)], because "not increased the joy" seems opposite to what immediately follows, "they joy," etc. Hengstenberg retains not (the Kethibh reading) thus: 'Thou hast multiplied the nation (whose) joy thou hadst not increased' - i:e., 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 explains it, The prophet sees in vision a shifting scene, comprehending at one glance the history of the Christian Church to remotest times-a land dark and thinly populated, lit up by a sudden light, filled with new inhabitants, then struggling with difficulties (so the English version, "Thou hast multiplied the nation, and (soon after) not increased the joy"), 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. Some suggest to read hagil, "Thou hast multiplied the joy, Thou hast increased the gladness" (hasimchah), corresponding to the two kindred verbs following, They are glad ("They joy"), samchu and yagilu, "men rejoice." They joy before thee according to the joy in harvest - a phrase taken from sacrificial beasts; the tithe of harvest was eaten before God (Deuteronomy 12:7; Deuteronomy 14:26, "thou shalt eat there before the Lord thy God, and thou shall rejoice, thou, and thine household").
As men rejoice when they divide the spoil - referring to the judgments on the enemies of the Lord and His people, which usually accompany revelations of His grace. The future joy of the elect nation because of its deliverance from its oppressors.