assuming an aural consistency of the translator of the old french into old english, if "newyn" is "known" then "stewyn" is "stone"

i.e. to sing in molded stone - refers to the exactness of what has preceded or will follow. i think, too, that "monkes" may refer more to the travelling singing troubadors who would sing epics such as 'la morte d'artur', but given the religious context (ihesu (jesus?)), the word "monkes" was used instead.

it is common in medieval epics to include a verse like this at the beginning and end of the poems, a way of saying, "this is the truth."