Published in response to Bishop John Maxwell's "Sacro-Sancta Regum Majestas", it was intended to be a comprehensive defence of the Scottish Presbyterian ideal in politics.
The book defends the rule of law and the lawfulness of defensive wars (including pre-emptive wars) and advocates limited government and constitutionalism in politics and the "Two Kingdoms" theory of Church-State relations (which advocated distinct realms of church and state but opposed religious toleration).
After the Restoration, the authorities cited Rutherford for high treason, but his death intervened before the charge could be tried.
[citation needed] The attack on absolutism, the defence of the rule of law and the emphasis on the importance of the covenant made Lex, Rex a precursor to the social contract idea, and helped pave the way for the political theory of John Locke.
However, Rutherford's views on Church-State relations and his opposition to religious toleration were not shared by Locke.