The phrase “holy, holy, holy” is an important one that occurs only twice in the Bible. On both occasions, the phrase comes from heavenly beings to those receiving revelation from God.
In the Old Testament, Isaiah experiences God in the Jewish temple. We read, “In the year that King Uzziah died I saw the Lord sitting upon a throne, high and lifted up; and the train of his robe filled the temple. Above him stood the seraphim. Each had six wings: with two he covered his face, and with two he covered his feet, and with two he flew. And one called to another and said: ‘Holy, holy, holy is the Lord of hosts; the whole earth is full of his glory!'” (Isaiah 6:1-3). Seraphim are heavenly creatures specifically mentioned only here in the Bible.
The other occurrence of this phrase in the Bible is in Revelation 4:8. There, John writes of what are likely the same heavenly beings seen by Isaiah. John records, “And the four living creatures, each of them with six wings, are full of eyes all around and within, and day and night they never cease to say, ‘Holy, holy, holy, is the Lord God Almighty, who was and is and is to come!'” In both John’s and Isaiah’s visions, these beings constantly declare God’s glory.
The emphasis of the phrase “holy, holy, holy” is clearly on the holiness of God, but what does this mean? The holiness of God refers to His being “set apart” or distinct from all of creation. The word holy is used more than 600 times in the Bible. It describes something or someone set apart from all else. For example, the seventh day was called “holy” and set apart as special by God in Genesis 2:3. The garments of Israel’s priests were considered unique and holy (Exodus 28:2). God is distinct from creation, being the Creator of all things (Genesis 1:1). God is “set apart” in the sense that He is separate from sin, corruption, and impurity. He is perfect in all ways.
He is exceptional, in a category by Himself, unmatched by any other being or thing in the universe.
Finally, repeating a word three consecutive times held an important value in the Hebrew language. The repetition makes it stand out as important. We have a similar practice in English, as seen in the phrase “far, far away”; the repetition of far provides emphasis. The fact that the word is repeated three times indicates a state of completion or absoluteness. In both Isaiah and Revelation, the word holy is used three times to emphasize God’s holiness and to convey the completeness of it.