"If I can unite in myself the thought and devotion of Eastern and Western Christendom, the Greek and the Latin Fathers, the Russian and the Spanish mystics, I can prepare in myself the reunion of divided Christians. From that secret and unspoken unity in myself can eventually come a visible and manifest unity of all Christians. If we want to bring together what is divided, we cannot do so by imposing one division upon the other. If we do this, the union is not Christian. It is political and doomed to further conflict. We must contain all the divided worlds in ourselves and transcend them in Christ." ~ Fr. Thomas Merton 1915-1968

"The signature of God is One" Fr. Lawrence Vadakkan
Miraculous Icon
of Christian Unity

Our Lady of Soufeniah
(Damascus, Syria)
weeps for sorrow because
of division within the Church.

film of the tears flowing from the eyes of the Virgin

Our Lady of Perpetual Help
The Feast of Mary Mother of God was instituted by Pope Pius XI in 1931 in view of fifteenth centenary of the Council of Ephesus. Oct.11, 431 AD was the date historians believed to have been the date of the close of the the Third Ecumenical Council. In the Council of Ephesus Mary was proclaimed Theotokos the Mother of God.
Mary is devoutly honored as Theotokos in the Eastern Church, and the pope, in instituting the feast, asked prayers for Christian unity.
The feast day was moved by Pope Paul VI to January 1, Solemnity of the Mother of God.

Christ's Prayer for Christian Unity ~ Matthew 28:2-51
copper-plate engraving from a French edition (1693) 
of an illustrated religious book originally published in 1593

Christ's Prayer for Unity

Matthew 28:18,  John 5:20,  and John 17:2 recount the post Resurrection account of Christ sending forth the Apostles on Mt. Tabor where He prayed to the Father for Christian Unity:

John 17: 20-24
After blessing the Apostles who will carry the Gospel into the world, Jesus prays to the Father for us all:

20 Neither pray I for these alone, but for them also which shall believe on me through their word;

21 That they all may be one; as thou, Father, art in me, and I in thee, that they also may be one in us: that the world may believe that thou hast sent me.

22 And the glory which thou gavest me I have given them; that they may be one, even as we are one:

23 I in them, and thou in me, that they may be made perfect in one; and that the world may know that thou hast sent me, and hast loved them, as thou hast loved me.

24 Father, I will that they also, whom thou hast given me, be with me where I am; that they may behold my glory, which thou hast given me: for thou lovedst me before the foundation of the world.

Barnes' Commentary:
"Neither pray I for these alone ..."   Not for the apostles only, but for all who shall be converted under the preaching of the gospel. They will all need similar grace and be exposed to similar trials. It is a matter of unspeakable joy that each Christian, however humble or unknown to men however poor, unlearned, or despised, can reflect that he was remembered in prayer by "him whom God heareth always." We value the prayers of pious friends. How much more should we value this petition of the Son of God! To that single prayer we who are Christians owe infinitely more real benefits than the world can ever bestow; and in the midst of any trials we may remember that the Son of God prayed for us, and that the prayer was assuredly heard, and will be answered in reference to all who truly believe.
All may be one - May be united as brethren. Christians are all redeemed by the same blood, and are going to the same heaven. They have the same wants, the same enemies, the same joys. Though they are divided into different denominations, yet they will meet at last in the same homes of glory. Hence they should feel that they belong to the same family, and are children of the same God and Father. There are no ties so tender as those which bind us in the Gospel. There is no friendship so pure and enduring as that which results from having the same attachment to the Lord Jesus. Hence, Christians, in the New Testament, are represented as being indissolubly united - parts of the same body, and members of the same family, Acts 4:32-35; 1Co. 12:4-31;Ephesians 2:20-22; Romans 12:5.