One of the shortest, yet for me most influential, books I have read is The Law, written by Frédéric Bastiat in 1850, shortly before his death. Frédéric Bastiat was a member of the French Assembly, classical liberal theorist, and political economist.
In The Law, Bastiat explains how the powers of society are derived from the God-given rights of man. The purpose of law should be to institute justice. An extension of the powers of government into philanthropy would, he posits, counter the primary purpose.
Bastiat decries what he calls "legal plunder" and the tendency of legislatures to consider themselves wiser than the populace--except during election time.
To date, this brief explanation of the role of government is the best I have encountered, and I recommend it to anyone interested in political science. I enjoyed Bastiat's writing style thoroughly, and after reading The Law, went on to read every book and essay of his that I could find.