Abraham Lincoln carried in his pocket a spiritual book of days, titled A Believer's Daily Treasure, which was originally published in the mid-1800s by the Religious Tract Society of London, England. There is speculation that the devotional may have been given to Lincoln by his wife Mary. Applewood's 2015 edition of the book includes an introduction by Carl Sandburg, which was first published in a 1957 edition. Said Sandburg, "... it is new testimony that he was a man of profound faith."