In this video, R. C. Sproul explains that the Bible talks the most about God's holiness.
Many words are used to describe God, but there's only one that is repeated in succession when the Bible describes God. In the English language, exclamation points, italics, bold, all are used to call attention to something of particular importance. When the Jews wanted to emphasize the importance of something, they used repetition…There is only one attribute of God that is raised to the third degree of repetition by the angels in the Bible and it is the attribute "holy.
"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!” (Is. 6:1-3)