In his remarks, Cardinal O'Malley stressed the call to be missionary disciples.
The fundamental decision to love is born from an encounter with the living God, who first loved us, he said. In this encounter, we can see the world through God's eyes and recognize what is truly beautiful and important in life.
Our response to that encounter is how we live out discipleship, the cardinal said.
"Pope Francis makes it clear that our call to discipleship is a call to be missionary disciples. We're faithful to our mission as Christ's family only by inviting others to be a part of that mission, by helping families to become what they are."
Family is critical to achieving this goal, Cardinal O'Malley said. "In God's plan, the family is the school of love where we learn to make a gift of ourselves."
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He emphasized that "marriage in God's plan is the sanctuary of love" and "families are missionaries - they pass on the faith to new generations."
"The parents not only communicate the Gospel to their children, but from their children they can receive the same Gospel, deeply lived by them. Such a family becomes an evangelizer of many families."
Those families that live out this mission "change the course of history," Cardinal O'Malley said. "They open the door that allows God's light to enter the world and their witness helps us to be open to life."