VATICAN CITY, JAN. 18, 2004 ( John Paul II made an urgent appeal to underline the start of the Week of Prayer for Christian Unity.

In "a world thirsty for peace, it is urgent that the Christian communities proclaim the Gospel unanimously," the Pope said. "It is indispensable that they witness the divine Love that unites them, and that they be bearers of joy, hope and peace, becoming leaven of new humanity."

The Holy Father made his appeal today, from the window of his study, before praying the Angelus with several thousand pilgrims, gathered at midday in St. Peter's Square.

The Pontiff reminded the pilgrims that the theme of this year's Week of Prayer is Jesus' words "My peace I give to you."

The program for the week was written by the Christian confessions that live in Aleppo, Syria, as instructed by the Pontifical Council for Promoting Christian Unity and the World Council of Churches' Faith and Order Commission.

"It is significant that the theme was proposed by the churches of the Middle East, where unity and peace are the most acutely felt priorities," the Pope said in a clear voice.

During the next eight days, Christians of various confessions and traditions will gather to pray for reinforcement "of their common commitment to full unity," John Paul II said.

The program, written by Syrian Catholics, Orthodox and Protestants, offers prayers for each day of the week in which Christian representatives around the world will gather in ecumenical meetings.

The Pope emphasized that Christians "feel acutely the need to turn to their only Lord, so that he will help them to overcome the temptation to discouragement in the difficult path which leads to full communion."

The Holy Father concluded by calling on the intercession of the Virgin Mary so that this Week of Prayer will "bear copious fruits for the cause of Christian unity."

"May it be a propitious occasion for those who believe in Christ to exchange a fraternal embrace, in the peace of the Lord," he added.

The Week of Prayer for Christian Unity originated in the Pentecostal Movement in Scotland with ties in the United States. In 1894, Pope Leo XIII encouraged the practice of the Octave of Prayer for Unity in the context of Pentecost.

Cardinal Walter Kasper, president of the Pontifical Council for Promoting Christian Unity, officially inaugurated the week's celebrations in Rome. He presided at an ecumenical ceremony today in St. Bridget's Church, together with the Lutheran bishop of Helsinki.

Cardinal Kasper will close the Week of Prayer next Sunday with a liturgy in the Basilica of St. Paul Outside the Walls.