We had a minister mainly because he was a friend of ours but also because we felt a registrar's service was fairly perfunctory, neither of us had liked the civil ceremonies we had been too. Neither of us are remotely religious either.
There was a certain amount of religious content as in we had to have hymns and he did a sermon but he was pretty sensitive about the fact that we weren't really christian and the theme he chose to speak on suited us very well. The hymns were fairly non-religious too, as far as hymns can be anyway

and were both tunes I already knew and liked.
To be honest though, i have to say on the day i barely noticed the religious tone!