The two uses of text refer to different meanings. For example, among the definitions of text provided by Collins are
1.the main body of a printed or written work as distinct from commentary, notes, illustrations, etc
2.the words of something printed or written
3.[often plural] a book prescribed as part of a course of study
When you say the remainder of the text . . . you are referring to a singular thing, and definition 3 seems the best fit.
When you say the remaining text [of the book] . . . you are using it as a mass noun, and definition 2 seems to be what is meant.
The first form seems more appropriate since the sentence is discussing the overall body of the work rather than the particular words.