The Pope called for clergy to leave their comfort zones and tend to the needy on the peripheries of life.
He is on a five-day visit to Poland to mark the 1,050th anniversary of the country's adoption of Christianity.
He is also taking part in World Youth Day, a global celebration for young Catholics.
The Pontiff is due to attend a youth prayer vigil later on Saturday.
Pope Francis began his day with a visit to the Divine Mercy Sanctuary, consecrated by John Paul II during his last visit to Poland in 2003.
