In Revelation 4:8, this signifies that what the Word continually teaches is that the Lord Jesus Christ alone is God, and is alone to be worshipped. (Apocalypse Explained 285, Apocalypse Revealed 247)

285. And they had no rest day and night, saying, Holy, holy, holy, signifies that which is most holy proceeding from the Lord. This is evident from the signification of "had no rest day and night;" this, when it is said of the Lord's Divine Providence and guard, which is signified by "the four cherubim" that appeared as four animals, is universally and perpetually, since the Lord's Divine Providence and guard rest not and cease not to eternity. This is evident also from the signification of "Holy, holy, holy," as being that which is most holy proceeding from the Lord, for "holy" thrice named signifies most holy, for this reason, that "three" in the Word signifies what is full, complete, and continuous (See Arcana Coelestia 2788[1-13], 4495, 7715).

[2] The like is signified by this in Isaiah:

I saw the Lord sitting upon a throne, high and lifted up, and His skirts filled the temple. Above it stood the seraphim: each one had six wings; with twain he covered his face, and with twain he covered his feet, and with twain he did fly. And one cried unto another, Holy, holy, holy, Jehovah of Hosts; the fullness of all the earth is His glory (Isaiah 6:1-3).

The "seraphim" here have a like signification with the "cherubim;" and the throne high and lifted up" signifies the Divine proceeding from which is heaven; "the skirts that filled the temple" signify the Divine truth proceeding from the Lord in the ultimates of heaven and in the church; "the wings with which the seraphim covered their faces and their feet, and with which they did fly," signify the spiritual Divine in firsts and in lasts and the extension thereof on every side, thus omnipresence; "Holy, holy, holy," signifies what is most holy; that this is the Divine truth that fills all things is signified by "the fullness of all the earth is His glory. (That "glory" is the Divine truth, see above, n. 33 and that the Lord only is holy, and that "holy" is predicated of the Divine truth that proceeds from Him, see above, n. 204)