What is the aim of Spirit of the Laws by Montesquieu?

The primary focus of Montesquieu's work is to address the
issue of individual freedom and institutional control on a political science level. 
Montesquieu's work operates on a premise that seeks to analyze which form and structure
of government will work best in accordance to Enlightenment understandings of freedom
and individual autonomy.  His solution existed in the idea of divided government.  The
idea of seeing power in government as one domain that needed to be separated into
different branches with each portion containing a different function that is needed to
sustain government is vitally important to Montesquieu's work.  It argues that power is
more likely to be judiciously and cautiously exercised if government is configured in
such a manner where different aspects of power are divided and can be separated out into
other branches of government.