Die XVII Septembris MMX Benedictus XVI in Britanniam a Regina Elizabeth invitatus Missam Pretiosissimi Sanguinis hic celebravit fides in societate quod commodum fit beatifici J H Newman exemplo illustrans.
Oremus gives this translation of the last bit: "showing what advantage faith may be to society through the example of Blessed J H Newman".
I would express the sentiment in the purple bit by something along the lines of "rei publicae relligionem prodesse etc." ... if I had to.
But, frankly, I dislike the implication that 'Faith', meaning 'the Christian Faith', can be some sort of advantage or adornment or assistance to the post-Christian State or community. Of course, in a sense it is; but if your liner had been holed, and were going down fast, you wouldn't say "a lifeboat would be something of an advantage" unless you had iron nerves and couldn't resist going to your watery grave with an ironic litotes or meiosis on your lips. Individuals need Faith for Salvation; and states need the Kingship of Christ ... totally, urgently. Not as an advantage but as a necessity. And before SSPXers among you start crowing, I invite you to read the text of Pope Benedict's sermon, where you will discover that he says nothing remotely like what the 'translation' of the inscription alleges.
I don't like fides or societas in the senses apparent here; I don't understand the point of fit rather than est; and I don't like the quod ... construction. Apart from that ...