isaiah 9:4 For thou hast broken the yoke of his burden, and the staff of his shoulder, the rod of his oppressor, as in the day of Midian. - Free Bible Online

      4. The occasion of the "joy," the deliverance not only of Ahaz and Judah from the Assyrian tribute (2Ki 16:8), and of Israel's ten tribes from the oppressor (2Ki 15:19), but of the Jewish ChristianChurch from its last great enemy.
      hast--the past time for the future, in prophetic vision; it expresses the certainty of the event.
      yoke of his burden--the yoke with which he was burdened.
      staff of . . . shoulder--the staff which strikes his shoulder [MAURER]; or the wood, like a yoke, on the neck of slaves, the badge of servitude [ROSENMULLER].
      day of Midian-- (Jud 7:8-22). As Gideon with a handful of men conquered the hosts of Midian, so Messiah the "child" (Isa 9:6) shall prove to be the "Prince of peace," and the small Israel under Him shall overcome the mighty hosts of Antichrist (compare Mic 5:2-5), containing the same contrast, and alluding also to "the Assyrian," the then enemy of the Church, as here in Isaiah, the type of the last great enemy. For further analogies between Gideon's victory and the Gospel, compare 2Co 4:7, with Jud 7:22. As the "dividing of the spoil" (Isa 9:3) was followed by that which was "not joy," the making of the idolatrous ephod (Jud 8:24-27), so the gospel victory was soon followed by apostasy at the first, and shall be so again after the millennial overthrow of Antichrist (Re 20:3, 7-9), previous to Satan's last doom (Re 20:10).

JFB.