Charles Ellicott Commentary Revelation 15:4

"Who shall not fear, O Lord, and glorify thy name? for thou only art holy; for all the nations shall come and worship before thee; for thy righteous acts have been made manifest." — Revelation 15:4 (ASV)

Who shall not fear...—Rather, Who will not fear, etc. (the word “You” should be omitted, because You are holy. The word rendered “holy” is not that which is usually employed when the holiness of God is spoken of; it is a word which, when applied to men, denotes one who reverences the sacred obligations of natural and moral order, apart from the thought of mere law or custom.

The word is applied here, and in Revelation 16:5, to God, and denotes the recognition of those sacred obligations which the character of God, if I may say so with reverence, imposes upon Himself. It is the remembrance that God will, as Judge of all the earth, do right, and will vindicate the expectations of those who trust in His character, which generates a holy fear of Him.

All nations shall come and worship...—Translate, All the nations worship, because Your judgments (or, righteous acts) are manifested. The song is one in anticipation. The angels of judgment are going forth; the righteous dealings of God will be seen; but these things are spoken of as though accomplished: their completion is a divine certainty.