VATICAN CITY, JAN. 25, 2004 ( The quest for the full unity of Christians is an "imperative," John Paul II said as he urged the overcoming of "closed-heartedness."

At the conclusion of the Week of Prayer for Christian Unity, which gathered believers in Jesus Christ in ecumenical events worldwide, the Pope said that this challenge is one of the priorities of his ministry.

Jesus' wish that all Christians be united is "a binding imperative, the strength that sustains us, and a salutary rebuke for our slowness and closed-heartedness," the Holy Father said.

"The unity of Christians has been a constant desire of my pontificate and it continues to be a demanding priority of my ministry," the Pope said. "Let us never lessen our commitment to pray for unity and to seek it incessantly."

"Obstacles, difficulties, and even misunderstandings and failures, cannot and must not discourage us," he said. "Confidence in reaching, also in history, the full and visible communion of Christians rests not on our human capacities, but on the prayer of our common Lord."

In the afternoon, in the Basilica of St. Paul Outside the Walls, Cardinal Walter Kasper, president of the Pontifical Council for Promoting Christian Unity, was to preside, on behalf of the Pope, at the traditional ecumenical celebration of the closing of the Christian-unity week.