On Sept. 27, Pope Francis will visit the Philadelphia jail where I serve as one of the Catholic chaplains. What an unbelievable, once-in-a-lifetime, event. It brings to mind what I tell the inmates before the religious services I lead there:

"God loves to come through the barbed wire, concrete blocks, and our calloused hearts to show us that we are his sons and daughters. Nothing can keep him from loving you."

They look at me from mostly despairing faces and I wonder what they are thinking. I believe that this love of God the Father is what Pope Francis wants to show them during his visit on the morning before he celebrates Mass on Benjamin Franklin Parkway for a million people.

Why does the pope go first to the prisons in the cities he visits? He has said it many times himself, but I repeat it here because it might get lost in all the hoopla.

Pope Francis believes that the Christian Gospel calls us to imitate Jesus, who reached out especially to the marginalized, the outcasts in society, the lost sheep. This is how Francis sees those in prison. He sees the value and dignity God created in them and his heart goes out to them. The pope wants to hold these outcasts of society in his heart and ours when we celebrate the Body and Blood of Christ in the large community on the Parkway.

More than himself, he wants the Church itself to do this. He told a group of newly chosen cardinals earlier this year, "The way of the Church is precisely to leave her four walls behind and to go out in search of those who are distant, on the 'outskirts' of life." And as though to underline the outreach idea, "I prefer a Church that is bruised, hurting, and dirty because it has been out on the streets, rather than a Church that is unhealthy from being confined and from clinging to its own security." He especially wants those of us who are ministers not to be afraid to "smell like the sheep." A prison is likely to be such a place.

He takes this challenge further to include our relationship with Jesus himself: "We will not find the Lord unless we truly accept the marginalized. Truly, the Gospel of the marginalized is where our credibility is at stake, is found and realized." He wants us to have those cast aside or not even noticed in our hearts when we preach and teach. "The Church needs to be the 'voice of the voiceless'," he has said. This includes prisoners of course, but also refugees, the poor, even those the Church itself may push away in order to be pure. This is what Jesus did, standing up for the woman caught in adultery, for example. It would cost him.

But why does Francis stand up for those who have done wrong? Why reach out to those incarcerated for crimes against others, to those who broke the law?

Because that is the nature of mercy.

It is understandable to feel sympathy for the homeless, the sick, the hungry, and the refugee, but the imprisoned? The pope is reminding us that even Jesus wound up between two criminals on the outskirts of Jerusalem. There is no one who is outside God's forgiveness.

I believe that the pope is visiting the Curran-Fromhold Correctional Facility in Philadelphia to remind us that we are all in need of mercy, including himself. As he said to 4,000 inmates at a notorious prison in Bolivia this year, "The man standing before you is a man who has experienced forgiveness. A man who was, and is, saved from his many sins. That is who I am. I don't have much more to give you or to offer you, but I want to share with you what I do have and what I love. It is Jesus Christ, the mercy of the Father." Pope Francis offers them the Father's unconditional love, which he has received himself.

But is mercy only a one-way street? We might grasp that Francis is visiting the prison in order to forgive and to receive forgiveness — for himself and for the Catholic Church he shepherds. One could ask, "Receive forgiveness from prisoners? Only victims can offer forgiveness." But many of the inmates are victims too. They come from lives of hardships we can't begin to imagine.

What an astonishing reversal then, for inmates to embrace the pope and the Church he shepherds with this mercy too. The pope wants to experience this mutual reconciliation and oneness with these outcasts before he invites a million others on the Parkway to share this embrace of peace.

This forgiveness and communion, even with our enemies, is the hallmark of the Christian faith. It is embodied in the Lord's Prayer, "Our Father … forgive us our trespasses as we forgive those who trespass against us."

It will be a great day in Philadelphia indeed if we keep this embrace of the outcasts in mind when we roar a greeting to this humble and merciful pilgrim.

Father Paul F. Morrissey, Order of St. Augustine, is the author of "The Black Wall of Silence." Fr.Paul@blackwallofsilence.com