The Clerk himself is a quiet man, apparently faithful to his own calling, as Griselda is faithful to her husband. The host asks for a happy tale, and the Clerk obliges, although the happy part is long in coming.
The Clerk chooses an interesting character to exemplify the correct response to God's testing. Men were usually the heroes of the day--and the Clerk acknowledges this when he says, "Men speke of Job, and moost for his humblesse, As clerkes, what hem list, konne wel endite..." However, the Clerk chooses a woman--and a poor woman at that--to show two things: the penitent's response to God, and the responsibility of husbands to love their wives.
Both purposes are sounds Biblical doctrine which indicates that the Clerk, of all the religious people on the pilgrimage, may well be the "holiest" of all.