Chaucer asks his readers to thank Christ if there was anything in his book that they liked, because all good things proceed from him.
He also asks them to forgive him if there was anything that displeased them, for this was the fault of his "unkonnyng," or lack of skill. His intentions were good.
Chaucer says his true intent was to instruct people for their betterment.
He asks his readers to pray for forgiveness for him for anything that he wrote that did not meet this goal: all of his works except for his translation of Boethius's Consolation of Philosophy, saints' lives, and homilies.
He thanks Jesus and Mary for these holy works and asks that they send him the grace of penitence, confession, and penance for his sins, so that he can go to Heaven.