The earliest extant samples of connected (north) Estonian are the so-called Kullamaa prayers dating from 1524 and 1528. In 1525 the first book published in the Estonian language was printed. The book was a Lutheran manuscript, which never reached the reader and was destroyed immediately after publication.
What was the first Estonian language book to be published? (If the question is unanswerable, say "unanswerable")
a Lutheran manuscript