Sometimes we hear Protestants complain that arguments from fitness for some belief or other are invalid. For example, when we say that it was fitting that Our Lady’s virginity should have been preserved, Protestants get upset as though it proves nothing.
Here is something that that St Augustine has to say about arguments from fitness.
When this is known it will be as clear as it can be to men that all things are subject by necessary, indefeasible and just laws to their Lord God. Hence all those things which to begin with we simply believed, following authority only, we come to understand. Partly we see them as certain, partly as possible and fitting, and we become sorry for those who do not believe them, and have preferred to mock at us for believing rather than to share our belief. [Of True Religion, 14]
By his measure we would say (quite reasonably, I think) that an argument from fitness is not so certain as one based more upon reason. This fact does not mean that arguments from fitness are without any validity at all. Similarly, it seems clear that he does not consider them to be contrary to reason. Lastly, there is more than a hint here of St Anselm’s saying, “I believe in order that I may understand:” the pattern in the quotation above is to begin by believing what the Church teaches, and to move from there to understanding.
I concur with Augustine’s careful understanding of the usefulness of arguments from fitness (see another example here): they certainly aren’t as good as demonstration, but they are not without value, either. In any case, the purpose of this post is merely to highlight the fact that St Augustine stands in the long tradition of the Church in affirming the use of such arguments, and Protestants distance themselves from him when they reject them.