Setting out on the Lenten journey of conversion, Pope Benedict urged Christians to make a commitment "to take Jesus' side against sin and, as individuals and as a Church, to engage in spiritual battle against the spirit of evil."
In his main Angelus address March 13, Pope Benedict discussed the Gospel story of the temptation of Jesus in the desert.
The pope said the story is a reminder that evil and sin really do exist.
In modern societies where people pretend that God does not exist, it is logical that they do not think there is such a thing as sin or evil either, he said.
The pope asked Catholics for their prayers as he began his March 13-19 Lenten retreat led by Carmelite Father Francois-Marie Lethel, a theology professor and the secretary of the Pontifical Academy of Theology.