As everybody knew, the lives of saints were meant to mirror the life of Christ, so if you wanted to tell the truth about a saint, all you had to do was tell the truth about Christ.
Wish I'd had this to put before my grad seminar on medieval chroniclers a couple of years ago.This sort of thinking derived from the way that medievals read their Bible, which is to say, typologically. Things in the Old Testament were said to pre-figure or pre-incarnate the things in the New Testament. Jonah spent three days in a whale’s belly. Christ arose from the grave after three days. These two facts were not coincidental: Johan pre-figured Christ; he was a “type” of Christ. So if you want to know more about the Resurrection, you could always learn more about Jonah and the whale. Indeed, you can’t swing a dead cat in medieval exegesis without hitting an earlier dead cat that prefigures the very cat you’re swinging.
BTW, Got Medieval's author is blogging his thinking on the subject of his dissertation, namely Geoffery of Monmouth and Uther Pendragon, if you want to see a modern scholar at work.