The contrast between the "no" of man in the Garden of Eden and the "yes" of Mary at the Annunciation was the heart of Pope Francis' message for the Solemnity of the Immaculate Conception, which he said is an opportunity for each person to renew their own commitment to God.

When Mary says "I am the handmaid of the Lord" in response to the news that she will become the Mother of God, she doesn't say: "this time I will do the will of God, I am available, then I'll see," the Pope said Dec. 8, the Solemnity of the Immaculate Conception.

"Hers is a full yes, without conditions," he said, noting that at times, instead of imitating this attitude, "we are experts in the 'half-yes:' we are good at pretending not to understand what God wants and consciousness suggests."

We can also be "cunning" and avoid saying "a true and firm 'no' to God" by making excuses, such as "I can't," or "'not today, but tomorrow...tomorrow I will be better, tomorrow I will pray, I will do good, tomorrow."

However, by doing this "we close the door to good and evil profits from these missing 'yeses,'" Francis said, noting that each one of us has "a collection" of these missing yeses inside.

Each full and unreserved "yes" we say to God is the beginning of a new story, he said. Saying yes to God "is truly original, not sin, which makes us old inside."

"Have you thought about this? That sin makes you age inside? It makes you age right away!" he said, adding that "every yes to God begins a story of salvation for us and for others."

Pope Francis spoke to pilgrims gathered in St. Peter's Square for his Angelus address marking the feast in which the Church celebrates the Immaculate Conception of Mary, honoring the Catholic dogma that she was conceived without sin.

After reciting the Angelus, the Pope will as usual make his way to Rome's Piazza di Spagna, where he will lay flowers at the feet of the large statue of Mary Immaculate sitting in the center of the square, and recite a prayer of devotion to Mary.

He also announced that like last year, following his prayer in Piazza di Spagna he will go the Roman Basilica of St. Mary Major to venerate the ancient "Salus Popoli Romani" icon, traditionally believed to have been painted by St. Luke.

The Pope travels to the basilica before and after every international trip he takes in order to entrust the voyage to the care and intercession of Our Lady, typically with flowers in hand.

In his Angelus address, the Pope said the day's readings from Genesis and the Gospel of Luke point to two "critical passages" in salvation history which point to "the origins of good and evil."

Man's "no" to God at the very beginning is recounted in the passage from the Book of Genesis, which shows how "man preferred to look at himself rather than his Creator, he wanted to do his own thing, he chose to suffice with himself."

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."

(Story continues below)

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.

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."