Some see this letter as a step towards thinking of slaves as fully human. Before Paul, Ruden argues, a slave was considered subhuman, and entitled to no more consideration than an animal. Others think that Paul and the early Christians should have done more to combat the evil of slavery. In history, some Christians used the book to justify slavery. Pope Benedict XVI refers to this letter in the Encyclic, "Spe salvi", to tell of the power of Christianity to improve society. He says that Christianity was very important to the large decrease of slavery during the Middle Ages and after.