commonstyles.sty

\ProvidesPackage{commonstyles}

% always indent the first topic (paragraph) after a chapter heading
\RequirePackage{indentfirst}

% don't insert pagebreaks at new chapters
\RequirePackage{etoolbox}
\makeatletter
\patchcmd{\chapter}{\if@openright\cleardoublepage\else\clearpage\fi}{}{}{}
\makeatother

% format chapter headings to look like:
%
%            [I.]
% QUOD DOMINUS SIT DEUS CAELI.
%
\RequirePackage{titlesec}
\titleformat{\chapter}[block]%
    {\begin{center}}%
    {[\thechapter.]\\\MakeUppercase{\chaptername}}%
    {0pt}%
    {\MakeUppercase}%
    [\end{center}]%

% use roman numerals for chapters
\renewcommand{\thechapter}{\Roman{chapter}}

% don't display the word 'Chapter'
\renewcommand{\chaptername}{}

\newcommand{\caput}[1]{%
    \par% all chapters need to start a new paragraph
    \chapter{#1}%
}

\newenvironment{topic}[1]
    {%begin
        \par% always start a new paragraph for each topic
        \textbf{#1.}
    }
    {% end
    }

\endinput