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.
Later, celebrating mass in the nearby Sanctuary of John Paul II, he urged churchgoers to heed Jesus' call to be "on the move, a Church that goes out into the world".
"This call is addressed to us," he added. "How can we fail to hear its echo in the appeal of Saint John Paul II: 'Open the doors'?"
John Paul II, who was Pope from 1978 until his death in 2005, was a native of southern Poland. He was canonised in 2014 and relics are kept in the church that has taken his name.
Pope Francis' visit comes a day after he offered a private prayer at the former Auschwitz death camp.
He became the third Pope to walk through the main gate of Auschwitz, under its infamous inscription "Arbeit Macht Frei" - work sets you free.
Both his immediate predecessors, John Paul II and Benedict XVI, visited Auschwitz, but he preferred to stay silent rather than speak about the horrors which occurred there.