It had been a long day, and Father Andrew M. Greeley was frustrated and grouchy as he climbed into a hot cab with Mother Teresa. More than 30 years later, he still remembered their hour-long ride through southern Ohio.

"She was the happiest human being I had ever met," he recalled when she died in 1997.

Mother Teresa, now known as Blessed Teresa of Calcutta, might have been one of the most joyful people who ever lived.

Blessed Teresa of Calcutta might have been one of the most joyful people who ever lived.

No other saint spoke or wrote as much about smiling as Mother Teresa did. We always saw her smiling. Friends said she had a quick, often self-deprecating, sense of humor, and sometimes she'd double over from laughing so hard.

Even people like Father Greeley, who hardly shares her vision of Catholicism, couldn't help noticing how she always seemed happy.

But after she died and was put on the fast-track for sainthood, we learned how much we didn't know about her. In letters made public during her beatification process—letters she had wanted destroyed—we glimpsed the shadow-side of the smiling face she showed to the world.

We learned that at the start of her ministry she had heard the voice of Jesus and seen visions. In one, she was transported "as a little child" to Golgotha, where she stood with Mary at the foot of the cross and spoke with the dying Jesus.

We learned, too, that for nearly fifty years following those initial visions and locutions, Mother Teresa's prayer life was one of dark, pitiless silence. She lived her entire public life—all that time we saw her smiling and talking about joy—panicked that God had rejected her, or worse, that he was out there in the dark hiding from her.

In one of those long-secret letters, from 1957, she bared her soul to a spiritual director:

"In the darkness... Lord, my God, who am I that You should forsake me?.. I call, I cling, I want, and there is no one to answer... Where I try to raise my thoughts to heaven, there is such convicting emptiness that those very thoughts return like sharp knives and hurt my very soul... I am told God lives in me—and yet the reality of darkness and coldness and emptiness is so great that nothing touches my soul."

In the dark night

Other saints have confessed feelings of abandonment by God. In the sixteenth century, St. John of the Cross coined a phrase that now describes the experience—"the dark night of the soul." But we would be hard-pressed to find another saint who suffered a darkness so thick or a night so long as Mother Teresa.

To quote again from those long-secret letters:

In letters made public during her beatification process we glimpsed the shadow–side of the smiling face she showed to the world.

"They say people in hell suffer eternal pain because of the loss of God... In my soul I feel just this terrible pain of loss, of God not wanting me, of God not being God, of God not really existing. That terrible longing keeps growing, and I feel as if something will break in me one day."

But why would God permit such suffering in one who had given her life so completely to do his will? The answer may lie in the question.

We learned from her letters, that in 1942, while still serving as principal at a private girls' school in Calcutta, Mother Teresa had made a secret vow—"to give to God anything that He may ask, 'not to refuse Him anything.'"

God apparently took her at her word, and put her vow to the test. In 1946, when her locutions began, Jesus told her to quit her comfortable job and go serve the poor: "There are convents... caring for the rich and able-to-do people, but for my very poor there is absolutely none." She did what she was told. Then she didn't hear his voice again for another half-century.

As harsh and dreadful as it sounds, it's a pattern familiar in the Bible and in the lives of the saints. The servants of the Lord often undergo an ordeal, some test of their commitment and faithfulness. Think of Jeremiah or Hosea, or how much of the New Testament concerns suffering for the Lord's sake. "When you come to serve the Lord, prepare yourself for trials," the Book of Sirach says.

From her letters, we see that Mother Teresa understood herself to be enduring such a trial—a martyrdom less physical than psychological and spiritual.

Was it all an act?

For nearly fifty years following those initial visions and locutions, Mother Teresa's prayer life was one of dark, pitiless silence.

So, what are we to make of her happiness and joy—was it all a front, an act? There's no evidence of that. She appears to have been giving us a modern day, flesh-and-blood lesson in the meaning of Christian joy. The fact that while she was alive we never had any inkling of how much she suffered only makes her witness that much more challenging to our complacencies.

Mother Teresa wrote a lot about joy. It comes, she said, from being close to Jesus. Or as she put it: "Joy is a sign of union with God—of God's presence." Knowing what we now know about her feelings of divine rejection, this sounds like an inside joke, or a deliciously dark irony. But she had no guile about her. She always told us that joy wasn't a matter of attitude adjustment or putting on a happy face. Joy was hard work: "It is always hard, all the more reason why we should try to acquire it and make it grow in our hearts."

In the logic of the saints, which is the logic of the Scriptures, this makes sense. We're supposed to strive to get closer to Jesus, to become more like him. To imitate Jesus means to offer ourselves in love to God—to accept suffering and even death, as he did on the cross. St. Paul wrote that we should offer our bodies as "living sacrifices" to God.

The servants of the Lord often undergo an ordeal, some test of their commitment and faithfulness.

That's how Mother Teresa lived. Even the littlest task could be a beautiful sacrifice she offered to God. And she came to believe that her spiritual anguish was a sign of her deepening union with Jesus, a sharing in his experience of being forsaken on the cross.

This growing awareness, too, is reflected in her letters: "I have begun to love my darkness, for I believe now that it is a part, a very small part, of Jesus' darkness and pain on the earth."

The smile she flashed was genuine. It sprung from the joyful heart of one who had given herself to God completely.

God may have left her alone in the dark, but he gave her the grace and the faith to show us the light.

We'll find the joy we're all looking for only in surrendering ourselves to God in the service of our families and neighbors, she told us. It was a message we needed to hear in a culture that defines happiness as the self-centered pursuit of sensual pleasures and material comforts.

She taught us the secret of the first disciples—who rejoiced in their trials, and were thankful to be counted worthy to share in Christ's sufferings. "Remember," she told us, "that the passion of Christ ends always in the joy of the resurrection."

She showed us that joy could be a spiritual weapon, and that smiling could be an evangelical act.

“I have begun to love my darkness, for I believe now that it is a part, a very small part, of Jesus’ darkness and pain on the earth.”

Her joy was infectious, as Father Greeley discovered in that cab many years ago. She "opened up new horizons of possibility in my life," he said. "I knew that I could never be as good as Mother Teresa, but that I could be better than I was. I could be almost as radiantly happy as she was."

Mother Teresa once wrote: "Cheerfulness... is often a cloak that hides a life of sacrifice. A person who has this gift of cheerfulness often reaches great heights of perfection."

Now we know she was writing about herself. And about the kind of person God wants each of us to be.