I found the answer to this question mostly within a few lines on page 84,
“If nudity were going to represent anything good besides crude sexual desirability among the much-dressed Western Christian nations, art was going to be required to make it beautiful, strong, and apparently natural. Moreover, this transformation had to be accomplished in ways that expressed the beautiful truth of nudity and also allowed for the requisite sense of it’s shameful sexuality.”
In order to do this art had to represent the nude in a way that at the time was a symbol of beauty and strength. If the nude is depicted completely naturally it will only be sexual because the natural body has no other meaning beyond its physical charm. However, if the nude is placed within the context of clothing, then the nude can transcend sexuality, somewhat, and also be a beautiful truth. This is because the people of the times can unconsciously read the form of the body and relate it to clothing and it’s symbolic meaning. Clothing is able to go beyond the corruptibility of the body and be a comment on the spirit or eternal aspect of the figure. But a nude is still a naked body that can not escape its erotic nature. Later in the chapter it says,
“Nakedness, with its meaning enhanced by clothing, has lent itself to notions of ideal beauty and of natural reality, and it can express not only the loftiest abstract concepts but the most personal physical feeling.”
It is this representation of the vulnerable virtuous nude in such a way that it seems natural and true to life and yet becomes something more by subtly suggesting abstract ideas.