Just as their prospects were brightening, however, there came a severe blow in the death of their only son. Lucretia then gave up teaching and spent a great deal of time in the study of the Bible and of theology. She used to read William Penn, Dean Stanley, and John Stuart Mill with her baby on her knee. Soon she took her place as a preacher in the Society of Friends, feeling "called," as she tells us, "to a public life of usefulness"; and during the latter part of the year 1818, she accompanied another minister named Sarah Zane to Virginia, for the purpose of holding religious meetings. Here Mrs. Mott came into contact with the question of slavery, and in all her discourses she never failed to urge the doctrine of emancipation. She believed in liberty of the body and liberty of thought; indeed, her belief in liberty may be said to have been the basis of all her sermons. The Quakers who held slaves freed them as early as 1774. The Society of Friends, to which Mr. and Mrs. Mott belonged, became so interested in the slavery question as to recommend that any goods produced by slave-labor should not be handled by any Quaker in regular standing. Mr. Mott was at that time engaged in a prosperous cotton business, but consistent with his views, he gave up this business,—for a while finding great difficulty in making a living. In 1833, the Female Anti-Slavery Society was formed in Philadelphia. Mrs. Mott was one of four women who, braving public opinion, gave their voices to the cause of Freedom. She was President of the society during most of its existence; and it was due mainly to her inspiring presence, her courage and activity, and her unfailing dignity, that the society accomplished its great work. She sheltered fugitive slaves, everywhere befriended the colored people, and traveled from place to place preaching the doctrine of liberty. Young people of the present time can hardly understand the bitter and fierce opposition encountered by those people who were working to free the slaves. For many years, public feeling on the subject was so intense that many anti-slavery meetings were broken up by acts of violence. Sometimes mobs of men and women stoned the windows of the houses where these meetings were being held, breaking into the assemblage, leaping upon the platform, and shouting so loudly that the speaker's voice was lost in the noise. In 1838, during a riot in Philadelphia, a mob burned Pennsylvania Hall, and then marched through the streets threatening an attack upon the house of James and Lucretia Mott. Mrs. Mott sent her children out of the house to a place of safety, and she, with her husband and a few friends, sat quietly waiting for the mob. Before it reached the house, however, the leaders urged the rioters to attack a home for colored orphans in another part of the city, and so the raid upon the Mott house was given up for that night.