As you can probably infer from the title, this is an academic book intended for specialists in medieval religion. It assumes you have extensive prior knowledge of the subject and a reasonable grasp of Latin. Aside from those prerequisites, it is well written and as interesting as such a dry subject can be made.
Florilegia are collections for spiritual reading and moral edification.
Manipulus florum are tools for searching for quotes and references.
Tools of this sort emerged rather suddenly in response to the need for pastoral ministry and preaching. They were used by universities, priests, and mendicants. They were used primarily for preaching, but also for exegesis in school settings. For instance, one might look up a word and discuss the different meanins attributed to it.
The earliest were probably from schools in Paris, likely developed or inspired by the Dominicans, who thought religious tools should possess utiity, community, and anonymity.
By the mid-13th century, patristic texts had indices. Oxford invented in-line numbering, which was soon used in conjunction with column numbers. They developed standardized layouts for books and pages, and systems of references using Arabic numbers.
This is when alphabeticization was accepted as a standard arrangement of ideas. Medieval intellectuals were disposed to organize and body to things according to logic, which they felt reflected the harmony of God's creation. Alphabetizing denies this logic and reflects a growing utilitarian attitude toward books. This attitude also made people more willing to edit and excerpt texts.
Other layout developments ad useful signposts standardized* at this time include running headlines, marginal designations and notations, pargraph marking, and cross-references in non-glossed books.
*most were invented by Carolingian scholars but used in inconsistent ways.
If you're a church-goer, you're probably used to hearing sermons, but prior to this period those were mostly reserved by and for monks. Popes Alexander III and Innocent III, concerned about the popularity of Waldensianism and other heresies, ordered bishops to preach to their people, and also told bishops and abbots to live more humble and impoverished lives like the Waldensians were doing.
Cistercians specialized in this sort or missionary preaching.
The sermon records that are mostly likely to survive are those by university masters, who disseminated theirs. They also developed a new format, the "school sermon" where the structure was announced at the outset and then the listener was lead word by word through the text, with meaning being verified by scriptural quotations. Increasingly complex logic as employed. It was uncommon to use personal exempla. In other words, the sermons were more instructive and less emotional.
If you would like to see an example of this type of text, the Summa Guiotina (Sermones de tempore et de sanctis) can be downloaded from e-manuscripta.