God is knocking to come into people's lives, so be attentive, humble and courageous to let him in, Pope Francis said.
"When we feel in our heart: 'I want to be good, to be better ... I feel sorry for what I've done ...' This is Christ who is knocking," he said before praying the Angelus with those gathered Sunday in St. Peter's Square.
On the fourth Sunday of Advent, Pope Francis talked about Mary showing the way to be ready, humble, generous and courageous when God calls people in their lives.
Christmas is a time when Jesus returns again, "to knock once more on the heart of every Christian: He comes and knocks," the pope said.
"Each one of us is called to answer, like Mary, with a personal and sincere 'yes,' putting oneself fully at God's disposal, mercy and love.
"How many times Jesus comes by in our lives, and how many times he sends us an angel and how many times we don't realize it because we are too occupied, too wrapped up in our thoughts, our affairs and even -- in this period, in getting ready for Christmas -- and we do not realize that it is him who comes by and knocks on the door of our heart, asking to be welcomed inside," the pope said.
When people feel the desire to be better, nicer and closer to God and to others, "if you feel this, stop. It's the Lord who is there.
"Go pray and perhaps go to confession to clean up a bit, this is good for you," the pope said, but no matter what, do not miss the chance to open one's heart up to God.
"The precious gift of Christmas is peace, and Christ is our true peace. And Christ knocks on our hearts to give us peace, peace in our souls. Let us open the doors to Christ."