The essay analyses the onto-theological assumption of liberal thinkers' attitudes towards religion. Particularly, it will be shown that the division between a public and a private sphere and the subordination of spiritual to temporal right are determined by the onto-theological demonstration that religion does not concern the domain of truth, but that of obedience. The Author reconstructs this set of arguments moving from Baruch Spinoza's exemplary case, by taking into account the meaning and consequences of this conception of right for the following liberal theories. It is then discussed Rousseau's conception of the legislator and of civil religion, according to which the separation between religion and reason, theology and politics is translated into a real extraneousness. Here the religious factor is conceived both as a mean for securing stability and as a foreign body to be looked with suspicion.