For book-like classes,
\frontmatter disables the chapter numbering (but still adds unstarred
\chapter's to the TOC). The numbering is then resumed with
\mainmatter. (The reason for this is that chapters in the front matter, such as a foreword or preface, are typically unnumbered but should be listed in the table of contents.)
In the above the "Foreword" and "Preface" chapters are unnumbered but are listed in the table of contents. The "Dedication" chapter and the table of contents (which implicitly uses
\chapter*) are unnumbered and not included in the table of contents. The "Introduction" chapter is numbered (1) and included in the table of contents.