\documentclass[12pt, letterpaper]{book}
\usepackage{fullpage}
\usepackage{palatino}
\usepackage{color}
\usepackage[T1]{fontenc}
\usepackage[utf8]{luainputenc}
\usepackage{gregoriotex}
\usepackage{hyperref}
%\usepackage{parskip}
%\usepackage{changemargin}
\pagestyle{empty}

%\newcommand{\ssection*}[1]{%
%\section*[#1]{\centering\normalfont\scshape #1}}

\makeatletter
\renewcommand\section{\@startsection {section}{1}{\z@}%
                                   {-3.5ex \@plus -1ex \@minus -.2ex}%
                                   {2.3ex \@plus.2ex}%
                                   {\centering\normalfont\bfseries}}
\makeatother


\widowpenalty=10000
%\clubpenalty=5000

\begin{document}
\title{Music for the Roman Missal}
\author{ICEL}
\maketitle
\newcommand{\red}[1]{\textcolor{red}{#1}}
\newcommand{\black}[1]{\textcolor{black}{#1}}

\setspaceafterinitial{0mm plus 0em minus 0em}
\setspacebeforeinitial{0mm plus 0em minus 0em}

%\def\greinitialformat#1{%
%{\fontsize{43}{43}\selectfont #1}%
%}

\setgrefactor{17}
\grespaceabovelines=5mm

\begin{center}\begin{huge}\textsc{}\end{huge}\end{center}
\tableofcontents
\newpage
\includescore{ICEL.-full.tex}

\end{document}