Father Edmund Waldstein has posted some excellent writings explaining the pre-modern (classical and Christian) view of politcs and defending it from its ill-informed liberal detractors. I particularly recommend them to Orthosphere readers, even though I know by now you’ve all heard plenty of arguments against modern autonomy-worship, because Waldstein bases himself on an understanding of the common good that, although a part of our philosophical patrimony, has been all but forgotten. To sum it up
the human good is a participation in a higher, divine good. Thus our good exists not principally in our selves, but principally in the divine realm, and secondarily in ourselves. The divine good is more our own good than the good which exists in our own souls.
the community of men reflects God more than an individual man just as the universe reflects Him more perfectly than any one creature. Recall what I said about participation a moment ago: my own good exists more in the divine than in my individual existence; a corollary can now be seen: the common good, the order of the community, is more my good than any private good of mine. The common good of order or peace is common in fullest sense of the word: all the members of the community share it without it being divided or lessened by this sharing. Thus the common good is not merely a useful good; it is not merely the conditions that enable individuals to get what they want, it is the best good that individuals can have, it is that in which they find their happiness.
By the way, Waldstein is guided on this subject by the work of early twentieth-century Thomist philosopher Charles De Koninck, whose writings are one of those many Catholic intellectual resources that seem to have been thrown out and forgotten during the post-Vatican II deluge.