"You came out of yourself in prayer to encounter God, you came out of yourself in brotherhood to encounter your brothers and sisters, and you came out of yourself to evangelize, to give the good news," he said, adding that this announcement "is mercy in a world marked by desperation and indifference."
But simply talking about mercy isn't enough, "we have to bear witness, share and teach by going out of ourselves." Using a colloquial phrase, he said "we have to put the meat on the grill," otherwise people won't understand.
"This witness, of not being closed in on yourself, in your own interests, but going out, sharing with others" that God is good and is with us in life's most difficult moments, he said, "is the best message of mercy that one can give."
Turning to Justine, Francis said it was significant that she was baptized during the Year of Mercy, and that it was precisely on that occasion that "you found God and he allowed you to strip you of yourself."
Part of this process was "to go from being centered on yourself, to go outside to the joy of living for God and for others," he said, adding that "one of the characteristics of youth and of the eternal youth of God is joy."
Francis cautioned against the modern temptation to selfishness and narcissism, which he said only lead to sadness. "And joy is opposed to sadness. A sadness that is, precisely, what you went out from: self-referentiality."
"A young person who gets into themselves, who only lives for themselves, ends up in an 'impassioned self-referentiality,' full of self-referentiality," he said, and told the youth present to foster a healthy sense of humor about themselves, so they don't become too attached.
In reference to Matheus' testimony, the Pope said drugs are "one of the instruments that the culture in which we live has to dominate us." Because of this, an addict might feel the need "to be subtle, invisible to themselves, as if they were air."
Drugs, he said, "lead us to negate everything that roots us...it takes the roots out and makes you live in a world without roots, uprooted from everything; from projects, from your past, from your history, your homeland, your family, your love, everything."
After passing through an experience of being "invisible" and then becoming aware again, Matheus became conscious of God's plan, which is a plan "to console the pain of humanity," Francis noted.
Pope Francis also pointed out how Matheus said he wanted to discern his vocation during the upcoming Synod of Bishops on "Young People, the Faith and the Discernment of Vocation."
(Story continues below)
Subscribe to our daily newsletter
Each person has to discern their vocation "in order to see what God wants of us in light of our vocation," he said, and told participants to "give freely" of themselves and what they have received.
The Pope also spoke, as he often has, about the importance of the relationship between the elderly and young people. Talking directly to the older members of the community, he stressed the importance of dialogue with youth, telling them to "pass the torch, from the oldest to the youngest."
"One of the challenges that the world asks of us today is the dialogue between youth and the elderly," he said, telling participants that "I rely on your testimony" to carry this dialogue forward.
Elderly, he said, are not meant "to be kept in the closet, to be kept hidden," but are rather "hoping that a youth comes and speaks to them." And youth, he said, must take the dreams of the elderly and "redeem" them.
The elderly "have wisdom and they need (youth) to beat at their hearts for this wisdom," Pope Francis said, adding that "this dialogue is a promise for the future. This dialogue helps us to continue going forward."
Elise Harris was senior Rome correspondent for CNA from 2012 to 2018.