What does it mean to say that God is holy? Baruch Levine states on page 256 of his Jewish Publication Society commentary on Leviticus:
“The words of Leviticus 19:2 pose a serious theological problem, especially the second part of the statement: ‘For I, the LORD your God, am holy.’ Does this mean that holiness is part of the nature of God? Does it mean that holiness originates from Him? In the Jewish tradition, the predominant view has been that this statement was not intended to describe God’s essential nature, but, rather, His manifest, or ‘active,’ attributes. To say that God is ‘holy’ is similar to saying that He is great, powerful, merciful, just, wise, and so forth. These attributes are associated with God on the basis of His observable actions: the ways in which He relates to man and to the universe. The statement that God is holy means, in effect, that He acts in holy ways: He is just and righteous. Although this interpretation derives from later Jewish tradition, it seems to approximate both the priestly and the prophetic biblical conceptions of holiness.”
I have an easier time getting inspired by this definition of holiness than by the definition of holiness that has been in my mind for years: that God is separate from us.