You have enlarged the nation.
You have increased their joy.
They rejoice before you
as with the joy in harvest,
as men rejoice when they are dividing up the spoil. Bible other translations

“have enlarged...have increased.” God will enlarge the nation in the future, but also during the time of Isaiah, during the reign of Hezekiah, the land had been enlarged. However, the Hebrew text can also speak about it in the past tense as if it had already happened to emphasize that it will happen. This is the idiom of the prophetic perfect (see commentary on Isa. 9:1).

Commentary for: Isaiah 9:3