By doing this, man left his communion with God behind, "lost himself and began to fear, to hide himself and to accuse those around him," the Pope observed, explaining that once someone begins to accuse others like this, it means "you are distancing yourself from God" and "this makes sin."
However, instead of leaving man at the mercy of the evil done, he steps in and immediately looks for him, asking "where are you?"
This question, Francis said, is "the question of a father or mother who looks for their lost child...and this God does it with so much patience, up to the point of bridging the gap that has arisen at the beginning."
Pointing to the day's Gospel reading from Luke, which recounted the story of the Annunciation, the Pope said that Mary's "great yes" is what made it possible for God to come and live among us.
"Thanks to this 'yes,' Jesus began his journey on the path of humanity; he started it in Mary, spending the first months of life in the womb of his mother."
Jesus didn't come as an adult, already strong and full grown, but decided to follow the exact same path of the human being, doing everything in exactly the same way "except for one thing: sin."
Because of this, "he chose Mary, the only creature without sin, immaculate," he said, noting that when the angel refers to Mary with the title "Full of Grace," it means that from the beginning there was "no space for sin" inside of her.
"Also we, when we turn to her, we recognize this beauty: we invoke her as 'full of grace,' without the shadow of evil."
While the "no" of man at the beginning closed the passage from man to God, Mary's "yes" opened the path for God to be among us, Pope Francis said, explaining that Mary's response "is "the most important 'yes' in history."
"It's the faithful 'yes' that heals disobedience, the available 'yes' that flips the selfishness of sin," he said, encouraging attendees to use Advent as an opportunity to renew their own "yeses" to God, telling him "I believe in you, I hope in you, I love you; accomplish in me your good will."
"With generosity and confidence, like Mary, let us say today, each one of us, this personal yes to God," he said, and led pilgrims in praying the traditional Marian prayer.
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After the Angelus, he offered prayers for Indonesian island of Sumatra, which was hit by a 6.5 magnitude earthquake Dec. 7 that has so far left nearly 100 people dead.
"I wish to assure my prayers for the victims and for their families, for the wounded and for the many who have lost their homes. May the Lord give strength to the people and sustain the relief work."
Elise Harris was senior Rome correspondent for CNA from 2012 to 2018.