Here is the sixth in the series of short videos by Denis McNamara, Professor on the faculty of the Liturgical Institute, Mundelein; his book is Catholic Church Architecture and the Spirit of the Liturgy.
The columns represent important people within the Church who, metaphorically, support it, chief among them the Twelve Apostles. Before the Christian era, in Jewish architecture the columns represented the 12 tribes of Israel. Even within the classical, pre-Christian tradition, columns were identified with people, and different designs were ascribed to men, women and young girls. Building on both the Jewish and classical traditions that preceded them, we can see why it made great sense for the early Christians to incorporate the same symbolism into the design of their churches.
Because they are symbolic images of people, columns have particular aspects of design, again, incorporated into the tradition, and should not be just straight vertical lines that are pure structural support, as a modern architect might wish to do. This does not mean that every column should per force correspond precisely to the Doric, Corinthian and Ionic orders of classical architecture, but it does indicate the importance of columns of as symbolic images of people, and as decoration that visibly performs a structural purpose.
The question one might have after considering this is: even if we acknowledge that properly formed columns are right for a church building, do we need to have them in secular buildings as well, such as libraries, town halls, houses, theaters, and so on?
I would say that the church should be the symbolic heart of the community. Therefore, just as all human activity is formed by and leads us to the worship of God, so the design of all buildings, whatever their purpose, should be derived from and point to what should be the focal point within a town plan, the church, and so we ought to see columns in secular buildings too. All of this should be modified so that each building is appropriate to its particular purpose: a government building would have a design that corresponds more directly to that of a church, I would suggest, than the design of a cow shed or a public convenience.