Among the spiritual patrons of the event are two well-known eighty-somethings of the recent past: Pope John Paul II and Blessed Mother Teresa. Their benign, wrinkled faces will undoubtedly look down from banners upon the young participants, offering unspoken encouragement and inspiration.

Will the WYD organizers perhaps also display banners of these patrons when they were young? I bet participants would be intrigued to catch sight of the just-adult Karol Wojtyla and Agnes Bojaxhiu, looking like they just stepped out of the crowd on Sydney's Randwick Racecourse—their fresh faces expressing solidarity, as though to say, “See? We were young once. We too wanted to do great good and had to find the right path.”

Both these pictures come from the time when Agnes and Karol discovered their vocations. Agnes had just decided to become a nun; she left for the convent soon after this picture was taken, giving it to an aunt as a memento. Karol, photographed for a theater poster, was on the verge of rethinking his plans to be an actor.

In these pictures, we see two calm and serious young people gazing resolutely into the future. Thoughtful, clearly idealistic, untested—it would be a long time before anyone would call them “Holy Father” or “Mother.” Looking at them, we can't help wondering what started them on their paths. What impelled this young man and woman to answer Jesus' call so wholeheartedly?

Outside Influences. Both grew up in prayerful Catholic families—Karol in southern Poland, Agnes in Albania—at a time when these countries enjoyed independence. Each lost a parent—Karol's mother died when he was seven, and Agnes's father when she was nine.

Karol and his father ate together, prayed together, went for long walks, and sometimes rolled up the living room rug and kicked a soccer ball around. Agnes's mother often took meals to needy neighbors, with her little daughter at her side. Years later, Mother Teresa recalled her mother's saying: “When you do good, do it quietly, as if you were throwing a stone into the sea.”

Other people as well led Agnes and Karol toward their vocations. Agnes belonged to a high school youth group organized by Father Jambrekovic, the Jesuit pastor of her parish. When he got letters from Jesuit missionaries in India, he shared them with the teens. These vivid, enthusiastic stories from people caring for the impoverished and the sick caught Agnes's attention.

Karol encountered a different kind of young adult group in Cracow. The German forces that occupied Poland in 1939 imprisoned or murdered many priests. One short-staffed pastor turned to a devout layman—Jan Tyranowski, a tailor—to form a secret network of young people for prayer and mutual support. Tyranowski's deeply personal way of relating to Jesus made an impact. He “proved that one could not only inquire about God but that one could live with God,” John Paul later wrote. “I really received much from him.”

These years brought losses, too. Karol's studies came to a halt when the Germans closed the university in 1939 and sent its faculty to a concentration camp. His father died two years later, leaving Karol without any immediate family. “I never felt so alone,” he later recalled. A friend from that period, who described him as distraught, worried about what would become of him.

Signs of Struggle. Do these exterior influences shed light on the inner experiences that helped Agnes and Karol come to see and accept their vocations? Perhaps a little, though neither gave details.

Mother Teresa, in fact, systematically deflected attempts to probe her heart. “I was only twelve years old when I first felt the desire to become a nun,” she told a friend simply. “It is a private matter. It was not a vision. I've never had a vision.” Biographer Kathryn Spink wrote that it was “an intensely personal experience on which she would not elaborate.”

Whatever happened, it did not bring Agnes clarity about her calling. She thought and prayed about it for the next six years. At one point, she asked Fr. Jambrekovic how a person could know what God was calling them to do. The true sign is an experience of joy, he told her.

Agnes went through her teens uncertain about her future. There were times when she doubted whether she had a religious vocation, Spink reports. There may even have been times when she fought it. Eileen Egan, another biographer who knew Mother Teresa well, says that at first, she “did not want to become a nun and leave her family.” Perhaps we catch an echo of this reluctance in Mother Teresa's later remark to a journalist who asked whether, after caring for so many children of other mothers, she missed having her own child: “Naturally, naturally, of course. That is the sacrifice we make. That is the gift we give to God.”

For Karol too, it seems there was a struggle. By his own admission, he had no intention during his high school years of becoming a priest. Instead, Karol was strongly attracted to the theater, and this too was a serious mission. Defying the German occupiers, he and some friends invested themselves intensively in underground productions of Polish plays. It was a way of sustaining their fellow citizens' sense of humanity and national identity. It was also a form of cultural resistance that, if discovered, would have gotten them sent to a concentration camp.

Yet Karol began to sense a call to the priesthood as a more profound kind of resistance to the evil of the times. He later explained that “in the face of the spread of evil and the atrocities of the war, the meaning of the priesthood and its mission in the world became much clearer.” But responding to the light that beckoned toward the priesthood required a wrenching departure from his deeply felt commitment to the theater and his loyal circle of friends.

Alone with Jesus. Knowing that God's call provoked a personal drama in each of these young lives, wouldn't it be great to pull up a chair and watch the drama unfold? What went on in their minds and hearts as they weighed the factors and tried to discern whether they were really hearing God's voice? But here our curiosity comes up against a wall.

Both inner dramas played out in a theater without audience seating. Both took place on a stage with just two chairs drawn up opposite one another for a series of face-to-face conversations—between Jesus and Agnes, and between Jesus and Karol.

Agnes was fond of a chapel dedicated to Mary in a hillside shrine some distance outside of town. From time to time, her mother would arrange for transportation so that Agnes could pray there alone.

Poland also features numerous rural shrines but under enemy occupation, Karol had no opportunities for quiet retreats. He prayed in spare moments in unheated churches and in his apartment, lying on the floor with his arms stretched out in the shape of a cross.

Inner Light. Not even the people closest to Karol and Agnes knew what was happening in their secret conversations with Jesus. When Agnes announced her decision to become a missionary, her mother was caught off guard and retreated to her bedroom for an entire day of prayer. Karol's friends were stunned by his announcement that he was entering the archdiocese's underground seminary program. They tried hard to dissuade him.

From the outside, both dramas remain a mystery. What we do know is that as the hours passed in a silent chapel in the Albanian countryside in the late 1920s, and as the Klaxons of German police vehicles blared in the street below a Cracow apartment in the early 1940s, in the hiddenness of two human hearts, two of the most important decisions of the twentieth century were being made.

In the end, both Karol and Agnes emerged from their meetings with Jesus with a joyful sense of conviction. “A light was beginning to shine ever more brightly in the back of my mind: The Lord wants me to become a priest,” John Paul wrote. “One day I saw this with great clarity: It was like an interior illumination which brought with it the joy and certainty of a new vocation. And this awareness filled me with great inner peace.”

Agnes was eighteen when she understood clearly that she was to leave home to become a nun and pursue a vocation to the poor. As she told Kathryn Spink, she “became convinced that she was being called to 'belong completely to God. Our Lady of the Black Mountain at Letnice helped me to see this.' ” From then on, she said, “I have never had the least doubt of my decision.”

Jesus Is Calling. The privacy of the inner dramas of Karol Wojtyla and Agnes Bojaxhiu carries a message for all of us, whether we are at World Youth Day or somewhere else this month. It reminds us that something about each person's inner drama cannot be shared because there is something unique about each of us and God's relationship with us. We can find inspiration in how others have responded to Jesus' call, but his call to you and me is something we must discover for ourselves.

For each of us—in each of us—there is a theater without an audience, a stage with just two chairs, and an invitation to sit down for our own private conversations with the Lord.

Are you searching? Jesus invites you to pull up a chair and let the drama of your life unfold. Have you already set out on your vocation? He invites you to keep talking with him, so that he can help you to live out your call with confidence. The witness of faithfulness to your call may be the greatest help you can give those who are still discerning their own.

This is the encouragement John Paul II and Mother Teresa offer to young people in Sydney this month. Their aged faces on the banners show the signs of profound and often painful experience. Here is a man who came to know the church around the world in both its glory and its weaknesses. Here is a woman with hands-on knowledge of appalling human suffering. Yet at the end of their lives, their faces revealed the peace that comes from experiencing Jesus' presence along life's every road.

Kevin Perrotta is the author of Your Invitation to Scripture and How to Be Happy, a discussion guide to the Sermon on the Mount.