The University of Exeter Press is to be congratulated on producing this edition by D H Frost. While every phrase of Cornish, Latin, or Greek is translated into our current vernacular, I could not deny that this is a book one needs to burrow into in order to find the fun.
Essentially, it is a Cornish text perhaps dating from the 1570s, containing a catena of Patristic quotations on the Eucharist. What has fairly recently come to light concerns the origin of this Collection.
In 1554, 'Disputations' were organised in Oxford and other places in which Catholic and 'Evangelical' scholars debated Eucharistic doctrine. The evidential texts they brought into play were printed in the years after the Accession of Elizabeth Tudor by Foxe (him of the Martyrs). His book was widely circulated, partly through copies provided for reading in parish churches.
A writer with Catholic prejudices copied down from an edition of Foxe the Patristic texts used in these Disputations; this manuscript was later combined with the Tregear Homilies (a Cornish translation of homilies commissioned by Edward Bonner, restored Bishop of London in the 1550s, for use in the catechising of his diocese after the heretical teaching of the 1540s).
You may find it entertaining to imagine a covert Catholic propagandist, making use of a work printed in order to promote Protestantism, in order to refute that selfsame heresy.
Frost found more fun: in those Oxford Disputations, the Catholic Scholars threw at Thomas Cranmer quotation after Patristic quotation in which earlier writers had written in very 'realistic' terms about Christ's Presence in the Most Holy Eucharist; demonstrating, in instance after instance, that for 'the Fathers' the Eucharistic Elements were in absolute truth the Lord's Body and Blood.
Cranmer's replies are where much humour comes in. He argues, in effect, that the very strength of the language in which this reality is expressed means that an early Christian writer cannot really have meant to be taken literally.
And so when the 'Catholic' side provide yet more evidence of Eucharistic realism in the 'Patristic' period, Cranmer, far from capitulating, regards that evidence as further proof of his contention that such extravagance cannot really be meant literally.