In 1831, the Rollins family moved to Jackson County, Missouri. For a time, things were going well for the saints there, but soon persecution arose. She witnessed tar and featherings, and her own home was damaged by the mobs. But Mary stayed true to her faith (even, in an interesting twist of fate, turning down an offer from Lilburn Boggs to come and stay with his family and receive a good education in exchange for giving up Mormonism).
In July of 1833, a mob set on William Phelps' print shop, where the Book of Commandments were being prepared for binding. 15-year-old Mary and her 13-year-old sister Caroline were hiding nearby and watched as the Phelps were driven out of their home, their possessions ransacked, and the printing press shoved out a window and onto the street. Then, someone said "so much for the Mormon commandments," and dumped the manuscripts into a trash pile in the street. Mary, having had her own confirmation of the truth of these commandments, was determined to do her part to save them. Knowing full well what the mobs could and had already done to those that angered them, Mary and Caroline ran into the street, grabbed as many pages of the manuscript as they could hold, and took off running. The mob spotted them, and two men came running after the girls. Mary and Caroline climbed through a fence and hid in a thick cornfield. They laid the sheets on the ground and covered them with their own bodies. Mary states that although the men came close, they never did locate the girls and eventually gave up the hunt. The girls gave the manuscripts to Sister Phelps, and Mary eventually received a bound copy, which she "prized highly."
The portion that Mary and Caroline preserved cover (more or less) the beginning of our current Doctrine and Covenants to partway through chapter 64. They were "eagerly" quoted by missionaries, and were cited by church officials.
I'm grateful for Mary and Caroline's incredible courage and faithfulness. At age 15, Mary had received confirmation that the Book of Commandments was a sacred document, and put her life on the line to preserve what she could. She had a remarkable influence for good. On a personal level, I'm grateful that largely through her actions, I have access to these revelations. So many revelations that have strengthened my faith and given me encouragement are found in these chapters: guidance for receiving personal revelation; Emma being called to expound scriptures; confirmation of the Lord's love of the individual and the worth of souls; additional understanding about the atonement; the list goes on and on. While I know that no principle essential to our salvation would have been lost, I am grateful that Mary and Caroline risked so much so that we could have these words, and I cherish them all the more because I know their story.
Autobiography of Mary E. Lightner, Utah Genealogical and Historical Magazine, UG&HM 17 (1926).
Saving the Book of Commandments, Gospel Art Kit.
The Story of the Doctrine and Covenants, Robert Woodford