Isaiah 9:3

Thou hast multiplied the nation, and not increased the joy... — Better, following the marginal reading of the Hebrew: Thou hast increased its joy. The picture is one of unmingled brightness; the return as of a golden age, the population growing to an extent never attained before (comp. Isaiah 26:15; Jeremiah 31:27; Ezekiel 36:11), and scarcely admits of the dark shadow introduced by the reading of the text, unless, with some critics (Kay), we see in the words a contrast between the outward prosperity of the days of Solomon and Uzziah, in which there was no permanent joy, and the abundancy of joyfulness under the ideal king.

They joy before thee according to the joy in harvest... — The words “before thee” are significant. The gladness of the people is that of worshippers at a sacrificial feast (Isaiah 25:6; Deuteronomy 12:7; Deuteronomy 12:12; Deuteronomy 12:18), who find the secret spring of blessing in their consciousness of the presence of Jehovah. So the New Testament writers speak of “rejoicing in the Lord” (Philippians 3:1), of “joy in the Holy Ghost” (Romans 14:17). This “joy of harvest” represents the peaceful side of that gladness, thought of as the gift of God (Acts 14:17). But it had another aspect. It was the rejoicing after a conflict, historically with foes like the Assyrians, spiritually with all powers hostile to the true kingdom of God (Matthew 12:29). The joy of the conquerors on the battle-field, like that of harvest, had become proverbial (Psalms 119:162).