There wasn’t going to be a Part D, but there was. There wasn’t going to be a Part E, but now there is going to be. Because we keep getting new insight. The insight is coming because adopting an egalitarian theology brings a whole new aspect to Christian sexuality. The focus for it can be changed from being a male seeks female kind of focus, to one where sexuality is not just about relationships between men and women. Sexuality can actually be about relationships between individual believers and their Creator. For too long the church has lived in the shadow of Complementarianist theology which is basically the old patriarchy of society that most of the church followed for most of its history. Bring an Egalitarian eye onto the Christian worldview, and suddenly we can see a different understanding because we see godly women as more than just sexual playthings for men, and that shifts the whole nature of godly sexuality for both men and women.
So Part E is about to be written, and it will be on the topic of sexual devotion. That theme has been reflected upon throughout the series to date. It comes out of a conviction that sexuality is a gift from God and that there are ways of giving the gift back to Him, as worship. Married people obviously are doing this when they are sexually intimate together, but the single person can do this too. So that is what Part E is about.