What does Isaiah 9:3 mean?
The prophet has described a great darkness that is coming to cover the land of Israel (Isaiah 8:22). This is due to their unbelief in the Lord and their unwillingness to follow Him. That darkness will include the invasion and occupation by the Assyrians, but it will not end there.The darkness will not last forever, however. In His grace, the Lord will eventually send the light once more (Isaiah 9:2). Believers today know that Isaiah speaks of Jesus the Messiah as the one who will bring the light back to the land of God's people. As the Messiah, He will eventually free the people completely from their oppressors and return abundance to the nation.
Writing in the past tense of future events, Isaiah says that the Lord has "multiplied the nation". This would be an increase of the population. The Lord will also increase their joy. As well as their joy for abundant harvests and military victories. Isaiah describes a time when the nation will be thriving in safety, security, and plenty. The source of all of this will be the Lord.