"Honesty and sincerity of heart is not imposed on man by legal command or by the state's authority. It is an absolute fact that nobody can be constrained to a state of blessedness by force or law; to this end one needs godly and brotherly exhortation, a good upbringing, and most of all, a judgement that is independent and free.
"Therefore, as the sovereign right to free opinion belongs to every man even in matters of religion, and it is inconceivable that any man surrender his right, there also belongs to every man the sovereign right and supreme authority to judge freely with regard to religion, and consequently to explain it and interpret it for himself." - Baruch Spinoza, A Theologico-Political Treatise (1670)
As quoted by Austin Dacey in The Secular Conscience.