Why the Week of Christian Unity begins on January 18

Originally called the "Octave of Christian Unity," the week began with the traditional feast of the Chair of St. Peter, and highlighted his confession of faith.

Annually the Catholic Church, along with many other Christian churches throughout the world, celebrates the “Week of Prayer for Christian Unity” from January 18 – 25.

In recent years it is always explained that this week concludes on the feast of the Conversion of St. Paul on January 25. However, it is often forgotten that this week began on a feast of St. Peter, called the Chair of St. Peter at Rome, once celebrated on January 18.

Many Anglicans continue to celebrate a similar feast on that day called the Confession of St. Peter, focusing on the confession of faith that St. Peter gave in support of Jesus’ divinity.

The choice to begin a week of prayer for Christian Unity on January 18 was a deliberate one, made by Fr. Paul Wattson, regarded as the “founder” of this week.

Octave of Prayer for Christian Unity

A 2008 article in L’Osservatore Romano explains how it came about.

Fr. Wattson’s English friend Spencer Jones suggested that there be an annual day of prayer and preaching on the office of the papacy. He mentioned that June 29, the Feast of St. Peter, would be a very appropriate day for this devotion.
Replying to Rev. Jones on 30 November 1907, Fr. Paul wrote: “The ‘Peter sermon’ suggestion is fine. In addition to that, what do you think of inaugurating a Church unity week beginning with St. Peter’s Chair at Rome, 18 January, and ending with St. Paul’s Day?“

This became known as the Octave of Prayer for Christian Unity, and was eventually approved by Pope Pius X in 1916.

The week, framed by these two feasts, highlights the foundation of Christian unity, built firmly on the faith of St. Peter and strengthened by the writings and example of St. Paul.