An emphasis on Gildas's De excidio as a jeremiad has reinforced a perception of the De excidio as a failed intervention. Indeed, Gildas begins his letter by invoking the lamentations of Jeremiah over the fall of Jerusalem and the destruction of her temple:

He ends his letter, however, by summoning the more active and reformist ‘call to arms’ of Jeremiah's contemporary, Ezekiel, whom God had installed as the speculator or watchman for his people:

In offering, at the last, a ‘plank’ to the Christian leaders of Britannia, Gildas emphasised his role as a speculator within an Old Testament Israel where kings, priests, and prophets shared responsibility for protecting her people. That this model of authority offered in the De excidio – where the monastery provided holy men as speculatores – was successful in the British Isles is most clearly seen with the pastoral mission of the Irish peregrinus Columbanus to the continent at the end of the sixth century. Operating in both Gaul and Italy, Columbanus was confident in his ability to establish monastic foundations in inhospitable regions lacking in ecclesiastical infrastructure, and in his ability to edify volatile kings and territorial bishops lacking in moral leadership.