SAT Text Structure and Purpose Question

The following text is adapted from Daniel Defoe's 1704 nonfiction book The Storm. The sermon is a sound of words spoken to the ear, and prepared only for present meditation, and extends no farther than the strength of memory can convey it; a book printed is a record; remaining in every man's possession, always ready to renew its acquaintance with his memory, and always ready to be produced as an authority or voucher to any reports he makes out of it, and conveys its contents for ages to come, to the eternity of mortal time, when the author is forgotten in his grave. Which choice best states the main purpose of the text?