The harvest season is immemorial and celebrated with customs that also become immemorial. In Armorica:
the last sheaf is consecrated as the Maiden;
a wether is chosen as Wolf of the Fold and sacrificed;
"...a branch hung with ears of grain [is] brought into house or barn."
-Poul and Karen Anderson, The Dog And The Wolf, Chapter XXIII, section 1, p. 451.
And the Church of England still celebrates Harvests. (Incidentally, there is a St Martin of Tours Church in Morecambe.)
Perhaps it is appropriate that, after the Harvest Festival in Armorica in 407, men harvest what they have sown politically. The locals expel the Romans. When Duke Gratillonius receives two Imperial delegates, Procurator Bacca and Bishop Bricius, the first two of these characters are fictional whereas the third is historical. In fact, four saints appear in The Dog And The Wolf:
Bishop Martinus, St Martin;
Martinus' kinsman, Sucat, St Patrick;
Martinus' successor, Bricius, St Brice;
Martinus' appointee to the ministry in Ys, Corentinus, St Corentin.
Of these, we respect all except the portly, expensively dressed Bricius, who puffs indignantly:
"'I will not demean my sacred office by squatting down like a savage.'" (p. 452)
Here is another change, and in a single generation, from the ascetic, unwashed Martinus to the lordly, self-important Bricius. The latter says that the Church is neutral in the civil war but that:
"'God will give victory to the righteous.'" (p. 453)
He will not or, at least, not necessarily - unless Bricius just means that he will prudently proclaim as righteous whoever wins? He also consigns Gratillonius to eternal torment instead of simply discussing the rights or wrongs of Gratillonius' case.
The characters act as they do because, like the Ysan leaders before the inundation or like James Blish's magicians after Black Easter, they know that they are living in changed times. In this case, Rome can no longer protect or compel so the Armoricans must take the initiative.