What does Isaiah 9:6 mean?

For--the ground of these great expectations, unto us--for the benefit of the Jews first, and then the Gentiles (compare "unto you," Luk 2:11). son . . . given-- (Psa 2:7). God's gratuitous gift, on which man had no claim (Joh 3:16; Rom 6:23). government . . . upon . . . shoulder--The ensign of office used to be worn on the shoulder, in token of sustaining the government (Isa 22:22).…

…The prophet tells us (Isa 9:6, Isa 9:7) they shall be done by the Messiah, Immanuel, that son of a virgin whose birth he had foretold (Isa 7:14), and now speaks of, in the prophetic style, as a thing already done: the child is born, not only because it was as certain, and he was as certain of it as if it had been done already, but because the church before his incarnation reaped great benefit and advantage by his undertaking in virtue of that first promise concerning the seed of the woman, Gen 3:15.…

For unto us a child is born,.... This is a reason of all that is said in the context; of the great light that shone upon and was seen by those that sat in darkness, and in the land of the shadow of death; of the great joy among the people; of the breaking off of the yoke, rod, and staff of the oppressor; and of the burning of garments rolled in blood, so putting an end to war, and establishing peace; all which is owing to the child here said to be born, by whom we are to understand the Messiah…