John Woolman's journal was not published until after his death. He wrote it primarily for his own personal reflection, though he undoubtedly also wanted to leave it behind as a document of his spiritual struggles.
Woolman was a Quaker, and central to the Quaker belief system was the idea that a person could have a direct relationship with God, without needing a priest or pastor to intercede. If a person was in direct relationship with God, dependent on that connection for spiritual guidance, it was important to do internal soul-searching and reflection. This helped insure that the voice one followed was truly God's rather the voice of the ego or other people. Journal writing was part of the traditional spiritual practices that helped people measure their spiritual progress, pour out and attempt to make sense of their spiritual conflicts, and confess their shortcomings.
Woolman was a devout Christian who wanted to reflect deeply on his life and his spiritual progress. His journal, because of his deeply felt and sincere spirituality, has been considered an American classic for several centuries. In it, Woolman struggled with his growing conviction that slavery was an evil that the Society of Friends (the Quakers) had to rid itself of to be in right relationship with God.
Much of his journal concentrates on the effort to oppose slavery and on how to humble his own soul to be an effective and gentle witness for God. He records in his journal how he often sought counsel from elders in how to approach slave owners and how, as he got older, he would insist on sleeping in slave quarters and paying slaves for the labor they did for him when he stayed with slave-owning families. He also writes often of how simple living on the part of those with power can make slavery less necessary and alleviate the burdens of the poor.
Woolman did not see slavery end in his lifetime, but not long after his death and shortly before the Revolution, the Quakers as a whole banned slavery among the faithful. Woolman's journal has been influential in America as an anti-slavery document and a testimony in favor of simplicity and the effectiveness of persistent, faithful devotion to social justice issues.