Augustinian againigan

I came across this Augustinian quotation heading a chapter called 'the Reasonableness of Faith' in Robert Louis Wilker's The Spirit of Early Christian Thought: Seeking the Face of God (Yale 2003):

Nothing would remain stable in human society if we determined to believe only what can be held with absolute certainty.

I'm missing something important here, as far as both Augustine and Wilker are concerned. Because nothing remaining stable is, surely, precisely the point of the Christian event -- no? The incarnation means: everything is different now. It comes to bring a sword, not to shore up stability. Or is this, counter-intuitively, precisely Augustine's point? (It's clearly not Wilker's).