Charles Ellicott Commentary Isaiah 26

In that day shall this song be sung ... —The prophet appears once more, as in Isaiah 5:1; Isaiah 12:4, in the character of a psalmist, and what he writes is destined for nothing less than the worship of the new city of the heavenly kingdom.

Salvation will God appoint for walls. —Better, salvation He appoints. The walls of the heavenly city are not of stone or brick, but are themselves as a living force, saving and protecting. The same characteristic thought appears in Isaiah 60:18.

Open ye the gates ... —The cry comes as from the heralds of the king of the heavenly city, proclaiming that the gates are open to those who are worthy to enter into it, i.e., to the righteous people who alone may dwell in the city of God (Psalms 15:1–2; Psalms 24:3–4; Psalms 118:19–20; Revelation 21:27).

The truth. —Literally, truths; all the many forms of truthfulness in heart and life.

Thou wilt keep him in perfect peace. —The italics show that the English version is supplemented with several interpolated words. More literally, and more impressively, we read, You establish a firm purpose; peace, peace, for in You is his trust. Completeness is expressed, as elsewhere, in the form of iteration. No adjectives can add to the fullness of the meaning of the noun.

For in the Lord Jehovah. —The Hebrew presents, as in Isaiah 12:2, the exceptional combination of the two names Jah (Psalms 68:4) and Jehovah. In the Hebrew for everlasting strength, we have, literally, the Rock of Ages of the well-known hymn. We have the same name of Rock applied to express the unchangeableness of God, as in Deuteronomy 32:4.

The lofty city, he lays it low ... —The “city” is probably the great imperial “city of confusion” that had exalted itself against God and his people. To that city, Moab, in all its pride, was merely a tributary.