And the LORD shall be king over all the earth: in that day shall there be one {k} LORD, and his name one.

(k) All idolatry and superstition will be abolished, and there will be one God, one faith, and one religion.

Wesley's Notes

14:9 In that day - All men shall agree in worshipping one God, in one way of spiritual worship, and hearty obedience.

Scofield Reference Notes

[1] king over all the earth

The final answer to the prayer of Mt 6:10. CF. Dan 2:44,45, 7:24-27. See "Kingdom (N.T.)" Lk 1:31-33 1Cor 15:28.

Jamieson-Fausset-Brown Bible Commentary

9. king over all . earth-Isa 54:5 implies that this is to be the consequence of Israel being again recognized by God as His own people (Da 2:44; Re 11:15).

one Lord . name one-Not that He is not so already, but He shall then be recognized by all unanimously as "One." Now there are "gods many and lords many." Then Jehovah alone shall be worshipped. The manifestation of the unity of the Godhead shall be simultaneous with that of the unity of the Church. Believers are one in spirit already, even as God is one (Eph 4:3-6). But externally there are sad divisions. Not until these disappear, shall God reveal fully His unity to the world (Joh 17:21, 23). Then shall there be "a pure language, that all may call upon the name of the Lord with one consent" (Zep 3:9). The Son too shall at last give up His mediatorial kingdom to the Father, when the purposes for which it was established shall have been accomplished, "that God may be all in all" (1Co 15:24).

Matthew Henry's Concise Commentary

14:8-15 Some consider that the progress of the gospel, beginning from Jerusalem, is referred to by the living waters flowing from that city. Neither shall the gospel and means of grace, nor the graces of the Spirit wrought in the hearts of believers by those means, ever fail, by reason either of the heat of persecution, or storms of temptation, or the blasts of any other affliction. Tremendous judgments appear to be foretold, to be sent upon those who should oppose the settlement of the Jews in their own land. How far they are to be understood literally, events alone can determine. The furious rage and malice which stir up men against each other, are faint shadows of the enmity which reigns among those who have perished in their sins. Even the inferior creatures often suffer for the sin of man, and in his plagues. Thus God will show his displeasure against sin.