Then shall the children of Judah and the children of Israel be gathered together, and appoint themselves one head, and they shall come up out of the land: for great shall be the day of Jezreel. The children of Judah and the Children of Israel - After the return from Babylon, the distinction between Israel and Judah was entirely destroyed; and those of them that did return were all included under one denomination, Jews; and the one head may refer to Zerubbabel their leader, and afterwards under Ezra and Nehemiah. In the more extensive view of the prophet the one Head may mean Jesus Christ, under whom the true Israel, Jews and Gentiles, shall be finally gathered together; so that there shall be one flock, and one Shepherd over that flock.
They shall come up out of the land - Assyria and Chaldea in particular; but also from the various places of their dispersions in general.
Great shall be the day of Jezreel - He alludes to the meaning of the word, the seed of God. God who has dispersed - sown, them in different lands, shall gather them together; and that day of God's power shall be great and glorious. It was a wonderful seed time in the Divine justice; it shall then be a wonderful harvest in the Divine mercy. He sowed them among the nations in his wrath; he shall reap them and gather them in his bounty.
Commentary on the Bible, by Adam Clarke [1831].