Okay, but Lewis likely had in mind the "natural law" account of morality (which I criticize below), and the Christian original sin doctrine, making secular progress impossible.

By contrast, I hold out the possibility of such progress that leads ultimately to transhuman glory.

https://medium.com/deconstructing-christianity/catholic-sanctimony-and-the-alleged-naturalness-of-moral-law-ea3b948aaaa1?sk=1df467a673d0c3231dd3bdb676d70b09