The Catholic Church of the Creator, to the Father, his prayer was uttered the day before he was to suffer “that they all may be one”, that is very dear, and hence that of Christ’s faithful are earnestly exhort to pray assiduously for the unity of Christians.

“In every age it has been the concern of the Roman Pontiffs, Our predecessors, and likewise it concerns Us greatly, that Christians who have, unfortunately, withdrawn from the Catholic Religion should at length be recalled to us as a forsaken Mother.  For in the Unity of the Faith the foremost characteristic of the truth of the Church shines forth, and it is thus that the Apostle Paul exhorts the Ephesians to preserve the unity of the Spirit in the bond of peace, by proclaiming that there is One Lord, one Faith, one Baptism (Ephes. 4:5).  With a glad mind, therefore, we have heard from the Society which is called “of the Atonement,” established in New York, that that prayers have been proposed to be recited from the Feast of the Chair of the Blessed Peter at Rome to the Feast of the Conversion of St. Paul, in order that this aim of Unity might be obtained from the Lord and at the same time we rejoiced that these prayers, blessed by Pope Pius the Tenth, of recent memory, and approved by the Bishops of America, have been circulated far and wide through the United States. And so, in order that the prayers above mentioned may be offered to God everywhere and with abundant fruit of the souls thus the desired end may be more easily attained, we, having also consulted our Venerable Brethren the Cardinal Inquisitors General of the Holy Roman Church, mercifully grant and bestow in the Lord a Plenary Indulgence and remission of all their sins to each and all the Faithful of Christ of either sex in the whole world, who from the 18th day of the month of January, the Festival of the Chair of Blessed Peter at Rome, until the 25th day of the same month, on which the Conversion of St. Paul is commemorated, shall recite every year once a day the prayers which are subjoined and on the last day of this Octave, truly penitent and confessed and refreshed with Holy Communion, shall visit any Church or public Oratory and there say these prayers to God for the concord of Christian Rulers, the extirpation of heresies, the conversion of sinners, and the exaltation of our Holy Mother the Church.  Moreover, we also grant permission in virtue of which confession may be made and Holy Communion received, and the visit be made in order to gain the aforesaid Plenary Indulgence, on the Feast of the Chair of Blessed Peter in Rome. Furthermore, to these same Faithful, who, with at least a contrite heart, say on any of the eight days named these same prayers, we grant an indulgence of two hundred days from the penances imposed upon them or owing by them in any other way, according to the usual form of the Church. We mercifully grant in the Lord that all these indulgences, remissions of sins, and relaxations of penances may be applied in behalf of the soul of the Faithful of Christ detained in Purgatory. This present Letter will be in force forever, anything to the contrary notwithstanding. The prayers, however, which are to be recited for the Unity of the Church during the Octave, we have ordained, as above, are to be as follows and lest any changes might creep into them, we have decreed that a copy of them is to be kept in the Archives of the Apostolic Briefs.”  ―Pope Benedict XV