They are primary because they are excerpts from the original book, which was written in this time, and people did use these medicines, and Medieval doctors did consult this book for their cures.
Spices were so hot because they meant that a person had wealth, because ordinary people could not afford spices. Medieval people valued spices because it meant wealth and also it was used for medicines. Spices could heal illnesses.
On page 1 of 4 What’s so Hot about Spices? It says “For a rich person, buying spices was one way to show off wealth.” Meaning if you had spices you