"All significant concepts of the modern theory of the state are secularized theological concepts." - Carl Schmitt, Political Theology (trans. George Schwab), p. 36
The essential argument here is that - for example - equality before the law is based on a secularized religious notion of Christian equality. I think there is something to do be said for this idea but it is a bit reductionist for my taste. More specifically it doesn't fully illustrate the radical difference between the modern and the ancient polity.