\documentclass{article}
\usepackage{listings} 
\newcommand{\readLST}[1]{%
	\begingroup
	\singlespacing
	\lstinputlisting[basicstyle=\footnotesize\ttfamily,breaklines]{#1}%
	\endgroup
}
\usepackage{setspace} 
\doublespacing
\begin{document}
blah blah blah blah blah blah blah blah
blah blah blah blah blah blah blah blah
blah blah blah blah blah blah blah blah

\readLST{listings3.tex}

blah blah blah blah blah blah blah blah
blah blah blah blah blah blah blah blah
blah blah blah blah blah blah blah blah
\end{document}