In St. Augustine's Confessions, Augustine explores his own journey to faith and in particular his own growing understanding of God and how he should respond as a result of who God is and what he has already done for him. As a result, the moral and societal expectations are placed firmly within this religious context, as Augustine experiences and understands more and more that God's call on his life results in expectations on how he should act morally and in society that could not be ignored. Note how he comments on this in the following quote:
I look forward, not to what lies ahead of me in this life and will surely pass away, but to my eternal goal. I am intent upon this one purpose, not distracted by other aims, and with this goal in view I press on, eager for the prize, God's heavenly summons. Then I shall listen to the sound of Your praises and gaze at Your beauty ever present, never future, never past.
For Augustine, obligations are all based around his Christian faith which calls Christians to live their lives now in the light of an eternity with God in heaven after death. All actions in the present are therefore based on this future, and moral and societal obligations are about doing what is right in order to move closer towards this future.
Moral and societal obligations, however, are presented very differently in Chaucer's The Canterbury Tales. Whilst there are characters who try to live respectable and upstanding lives, such as the Knight and the Prioress, at the same time the vast majority of characters clearly have their own agenda and are not burdened by the same moral and societal obligations that Augustine was. Just think of the content of some of the tales, for example, and the way that characters such as the Pardoner present themselves. The narrator is very open in pointing towards this different understanding of characters, as well:
The miller is a lout, as you're aware;
So was the reeve, and so were many more.
They both told bawdy stories. Then beware,
And do not lay upon me all the blame,
Or take in earnest what is meant in fun.
This text, in contrast with St. Augustine, presents the reader with a wide range of different understandings of moral and societal obligations, ranging from quite pious and principled approaches to characters who clearly live their lives very selfishly, doing what they think alone is important.