With her husband imprisoned in Liberty Jail, Emma Smith and her children were among the Latter-day Saints who made their way across northern Missouri to Quincy, Illinois, in the winter of 1839. This experience was vivid in her mind when she wrote to Joseph on March 7:
"I shall not attempt to write my feelings altogether, for the situation in which you are, the walls, bars, and bolts, rolling rivers, running streams, rising hills, sinking vallies and spreading prairies that separate us, and the cruel injustice that first cast you into prison and still holds you there, with many other considerations, places my feelings far beyond description. Was it not for conscious innocence, and the direct interposition of divine mercy, I am very sure I never should have been able to have endured the scenes of suffering that I have passed through, since what is called the Militia, came into Far West, under the ever to be remembered Governor's notable order. . . . We are all well at present, except Frederick, who is quite sick. Little Alexander who is now in my arms is one of the finest little fellows, you ever saw in your life, he is so strong that with the assistance of a chair he will run all round the room. . . . No one but God, knows the reflections of my mind and the feelings of my heart when I left our house and home, and allmost all of every thing that we possessed excepting our little children, and took my journey out of the State of Missouri, leaving you shut up in that lonesome prison. But the recollection is more than human nature ought to bear. . . . The daily sufferings of our brethren in travelling and camping out nights, and those on the other side of the river would beggar the most lively description. The people in this state are very kind indeed, they are doing much more than we ever anticipated they would; I have many more things I could like to write but have not time and you may be astonished at my bad writing and incoherent manner, but you will pardon all when you reflect how hard it would be for you to write, when your hands were stiffened with hard work, and your heart convulsed with intense anxiety. But I hope there is better days to come to us yet."
On March 19, less than two weeks after the failure of the second jailbreak attempt, Joseph Smith received his wife's letter, along with letters from his brothers Don Carlos and William, and from Bishop Edward Partridge. This correspondence called forth an immediate response. The following day Lyman Wight noted that the Prophet was "writing an epistle to the church, " and on March 21 Joseph wrote to Emma. The lengthy letter produced on March 20 was signed by all the prisoners in the Liberty Jail and contained sentiments that were later published as sections 121-123 of the Doctrine and Covenants. Although this epistle was addressed to the "church . . . scattered abroad and to Bishop Partridge in particular," Joseph sent it to his wife with instructions for his family to have the first reading and then convey it to the Church.
(Joseph Smith, The Personal Writings of Joseph Smith, compiled and edited by Dean C. Jessee, p.389-)
The full context of the Prophet Joseph Smith's letter can be found in Teachings of the Prophet Joseph Smith by Joseph Fielding Smith, pp. 129-148.