Pope Francis | facebook.com/PopeFrancisPage

The Week of Prayer for Christian Unity, alluded to in a recent announcement by the U.S. Conference of Catholic Bishops, kicked off earlier week. The conference issued a call to the faithful via social media.

"The Week of Prayer for Christian Unity is celebrated annually from January 18-25 to promote and encourage Christians around the world to participate in an octave of prayer for Christian unity," according to a Twitter post on Jan. 18.

The post linked to a page on the conference's website that includes the more than century-long history of the Week of Prayer for Christian Unity, when Christians worldwide take part in an octave of prayer for visible Christian unity.

"By annually observing the WPCU, Christians move toward the fulfillment of Jesus' prayer at the Last Supper, 'that they all may be one,'"  the conference's website says in a reference to the Gospel of John 17:21.

First observed in 1908 by Franciscan Friars and Sisters of the Atonement in New York, the WPCU grew into a worldwide observance in many nations and among millions of Christians who participate in an octave of prayer for Christian unity. In the northern hemisphere, the traditional WPCU period is Jan. 18-25.

For this year, the Middle East Council of Churches recited a verse from the Gospel of Matthew, "We saw the star in the East, and we came to worship Him." The verse highlights the Eastern Church tradition of celebrating the Epiphany in connection to the Baptism of Christ and the unity of all Christians through baptism.

On the evening before this year's Week of Prayer began, Pope Francis delivered an address to the Ecumenical Delegation from Finland, tying this year’s prayer theme to the theme of the Synod, "journeying together."

Last year's theme was from the Gospel of John, selected by the Monastic Community of Grandchamp in Switzerland, "Abide in my love ... You shall bear much fruit."