VATICAN CITY — Twenty-five years ago, her writings were banned by the Vatican and her legacy, a special devotion to the divine mercy of God, seemed in doubt.

Today she is a saint, her diary has been translated into more than a dozen languages and her Divine Mercy movement has attracted millions of Catholics around the world.

For St. Faustina Kowalska, it's been a remarkable reversal. And like several other sainthood stories in recent years, this one had a hidden protagonist: Pope John Paul II.

The Holy Father, who beatified her in 1993 and canonized her in 2000, was scheduled to go back to his Polish homeland Aug. 16-19 to inaugurate a $20 million basilica and pilgrim complex dedicated to St. Faustina and the Divine Mercy movement.

It's the latest chapter in the Pope's ongoing interest in the saint, who lived several years in John Paul's archdiocese of Krakow and died there in 1938 at age 33. As a young man in the same city, the Holy Father used to visit a sanctuary dedicated to her after her death.

After he became archbishop of Krakow in the 1960s, he pressed the Vatican for years to lift the ban on St. Faustina's writings. Convinced that Rome's opposition was based on a faulty translation of her diary, he had it retranslated — and the ban was lifted in 1978, six months before his election as Pope.

The second encyclical of his pontificate, Dives in Misericordia (Rich in Mercy), published in 1980, was dedicated to the divine mercy theme that drove St. Faustina's spiritual life.

Anyone who's ever waded through that papal text knows its language is not easy. Buttressed by a footnoted explanation of the linguistic and philosophical history of the concept of divine mercy, it explains how “in the eschatological fulfillment, mercy will be revealed as love.”

Anyone who's ever read St. Faustina's diary knows she wrote fairly simple thoughts, some based on her visions of Christ, who tells her plainly: “I have opened my heart as a living fountain of mercy. Let all souls draw life from it.”

While simplicity might not be the Holy Father's own writing style, he knows God sometimes speaks to the world through simple and uneducated people.

He has proclaimed a number of them saints in recent months, including St. Padre Pio, the Italian mystic, and St. Juan Diego, the Mexican peasant who had visions of Our Lady of Guadalupe.

St. Faustina's followers now call John Paul the “Mercy Pope,” and his support of the mystic nun goes back many years. As archbishop of Krakow, however, he sometimes had to temper the enthusiasm of her religious order, the Congregation of the Sisters of Our Lady of Mercy, who wanted him to fight the Vatican ban on Faustina's writings and get her sainthood cause rolling.

“They are bombarding me with requests to begin the process,” he said in 1965, according to his long-time biographer, Marian Father Adam Boniecki.

Then Archbishop Wojtyla did open the diocesan sainthood process and wrapped it up quickly, depositing the documentation at the Vatican in 1967. He figured the Vatican would be more open to dropping its ban on her writings once it had studied the beatification material.

At the same time, he cautioned his own priests against celebrating weekly Mass at the “altar of Mercy,” lest this be seen as promoting her cult.

“We are presently treading as if on glass,” he said of his delicate efforts to deal with the Vatican on the issue, according to Father Boniecki's biography.

The Vatican's attitude was dictated in part by the Church's longstanding suspicion of private revelations.

“The Church has always taught that revelation ended with the Apostles. For that reason, it has been deeply concerned not to give official credit to these presumed private revelations,” said Father Gianfranco Girotti, who worked at the Vatican's doctrinal congregation when the ban was in force.

In the case of St. Faustina, the imperative tone of some of the writings was also a factor. There was a “categorical” style to the diary entries that only added to the Vatican's caution, Father Girotti said.

Interspersed among the pages of the diary are warnings from Christ about dire consequences unless the mercy devotions are practiced and an annual Divine Mercy Sunday is established.

“I am giving them the last hope of salvation; that is, the feast of my mercy. If they will not adore my mercy, they will perish for all eternity,” one entry reads.

Part of that directive was fulfilled in 2000 when the Pope proclaimed the second Sunday of Easter as Mercy Sunday throughout the world.

St. Faustina wrote that she had witnessed a vision of Jesus — one hand raised in benediction and the other resting on his breast — from which emanated two rays of light. She said Christ demanded to have this image painted and venerated.

The image is now found in many churches around the world, including the Church of the Holy Spirit near the Vatican. The Holy Father visited that church and blessed the painting in 1995.

Some of St. Faustina's reported spiritual gifts set her apart from the Catholic mainstream. According to a Vatican biographical note, in addition to revelations and visions they included hidden stigmata, bilocation, the reading of human souls and prophecy.