I bristle when the notion of "the holy" is domesticated and the use of the phrase "the beauty of holiness," especially among Holiness people, seems to me generally to domesticate "the holy" to a kind of sentimentality. Further, another, mostly non-sentimental, idea "beauty" is quite prominent in Western intellectual history, largely due to the influence of Plato's *Symposium* (and his general metaphysics) and this history strikes me as quite contrary to the mode of thought and discourse in ancient Israel. Romanticism, which also drew deeply from the tradition of the *Symposium*, has degenerated here and there into sentimentality, though it is also still alive and well in its more respectable mode.
The point: Whether or not the phrase "the beauty of holiness" is a defensible translation of the Hebrew, the *idea* of the beauty of holiness must be tied to the idea of purity. There is a deep connection in the Western mind between beauty and wholeness. Although the vision of the world of ancient Israel is not to be conflated with this history, Israel, too, was hyper-concerned with wholeness. In order to come into the precincts of the holy God, one must be whole. Wholeness, to ancient Israelites, is not holiness, but wholeness is a condition required of people who are out to be holy. Impurity, i.e., the rupture of wholeness, is enough to make it impossible for one to become or remain holy, but in itself it is not holiness. God alone is holy and grants entry into and partaking of that holiness only freely, as a gift—and in ancient Israel that meant a gift to those who were pure and acted in accordance with a certain prescribed method of receptivity to God.
And so, "wholeness" is associated in ancient Israel with holiness, but only as a kind of equipping of one for the journey. Holiness, not wholeness, is the journey.
The idea of "beauty" in ancient Israel *can be thought* as linked to the idea "wholeness." And so, following this logic (independently of the question of translation), "the beauty of holiness" is a phrase that would describe not holiness itself, but what is associated with holiness. It would be similar to "the purity of holiness," "purity" not to be confused with "holiness," but associated with it, again, in ancient Israel.
In the gospel there is no condition for the hallowing of a human being except God's mercy, God's grace, and the human's openness to that grace. Indeed, the one at the heart of the gospel, Jesus, is—according to the gospel—to be thought always as crucified and crucifixion renders one utterly and hopelessly impure, un-whole, without beauty, one like the "suffering servant" of Isaiah 53.
This is not to say that there is no place for "purity" or "wholeness" or "beauty" in the gospel. However, that place is a very mysterious one, as Paul says when he speaks of "peace" (another term associated with purity), a beauty, we could say, that passeth understanding.
In other words, describing a certain view of human sexuality as “an expression of the beauty of holiness” is to take a stroll across a minefield. Human sexuality, by implication, according to the gospel, is holy insofar as it is enacted with openness to God's mercy.