The article discusses the most important premises which deal with Christian penance from the VI to the XI century. The main sources for the above article are the Penitential Books (Libri Poenitentiales), published as part of the series of Źródła Myśli Teologicznej (ŻMT 58), collected and edited by A. Baron and H. Pietras in 2011. The article consists of three parts. The first part examines the meaning of penance in the life of Christians as a medicine for sin which is an illness of the soul and the body. The second part presents the teaching of penitentials on the twelve ways of absolving from sins. The third part provides practical suggestions for confessors and penitents. The Penitential Books, as a witness to the development of penitential practices, confirm the role of individual spiritual therapy in the life of the Christian. This process of regaining of one’s spiritual health takes place, on one hand, through the grace of God’s Mercy, and, on the other hand, through penitential practices whose aim was internal conversion and outward change in one’s way of life.