All that we know about the book of Jasher is this, that there was such a book in Hebrew literature. Whether Jasher was the name of the author, or title of the book, is not certain. In various ancient languages the word used means "upright" or "just." In some ancient copies the sentence is omitted from Josh. 10:1313And the sun stood still, and the moon stayed, until the people had avenged themselves upon their enemies. Is not this written in the book of Jasher? So the sun stood still in the midst of heaven, and hasted not to go down about a whole day. (Joshua 10:13). The other books you refer to, such as the book of Nathan the prophet, etc., in the various scriptures, were uninspired books; or if inspired, were only for the then present use, and almost every vestige of these is now lost. The Holy Ghost did not inspire them for the people of God through all ages. There has been much discussion, and little profit, in these matters.
Suppose an absolutely perfect watch were given to a person—one that should go correctly through all time. The different parts have been made to order by many different persons, in different places, and wonderful and diverse machinery used in producing this perfect timekeeper. The owner of that watch would not need to be acquainted with the name, residence, etc., of each person employed by the designer and maker of that watch. Here, in this precious Book, the inspired Word of God, is the most wonderful production ever placed before the eyes of man. It not only unlocks and explains every secret thought of the heart of man—meeting his every spiritual need for time and for eternity -but it is the true and only full revelation of God to man. A great number of persons, in different places and conditions, have been used in producing this marvelous Book of books, every part being as important in its place as the wheels of a watch. God the Holy Ghost alone could have designed and executed this greatest treasure on earth. But this revelation is so wholly of God, that if we knew the minute history of every person employed, and the very day on which he wrote his part, it would not afford the smallest help; it is only (as we are assured you will agree with us) the divine Author that can, and does, enable us to understand and ever enjoy this inestimable treasure, for which we would ever praise God.