为什么诸如 \textit{}、\emph{} 等基本命令在我的文档中不起作用？

Question

\documentclass[a4paper, 12pt ]{article}
\usepackage{fontspec}
\usepackage{polyglossia}
%\usepackage[french]{babel}
\setmainfont{Lucida Grande}
\newfontfamily{\He}{SBL Hebrew}
\setdefaultlanguage{french}
\setotherlanguage{hebrew}

%\usepackage[ autospaceguillemets=true, autospacing=true, frenchfootnote=true]{polyglossia}
\usepackage{url}
%\MakeOuterQuote{"}
%\FrenchFootnotes
\newenvironment{mycitation}%
       {\begin{list}{}%
           {\setlength \rightmargin{\leftmargin}}%
            \item[]\makebox[0pt][r]{\guillemotleft}\ignorespaces}%
            {\unskip \makebox[0pt][l]{\guillemotright}\end{list}}
\newenvironment{sommaire}{\begin{center}\footnotesize \bfseries Sommaire %
       \end{center}\begin{quote}}{\end{quote}\par}
\begin{document}
\emph{Laudato}, \textit{VC} do not work ...etc

\end{document}