The reason why each and every one of us as Christians needs to play a part in the work for Christian unity is rooted in fidelity: Fidelity to the Church, to the Gospel, and to the Lord. That is why the Holy Father Pope Francis is going to meet Ecumenical Patriarch Bartholomew and other Christian leaders May 24-26. It is also why Cardinal Seán with Metropolitan Methodios of the Greek Orthodox Metropolis of Boston issued a joint letter to their clergy and faithful on May 21.

Vatican II taught us that Christian unity was one of its principal aims; that "The attainment of union is the concern of the whole Church, faithful and shepherds alike;" and that the work "extends to everyone, according to his or her talent" (Decree on Ecumenism, 1 and 5). Just like in evangelization, the Church has no superfluous personnel.

And the link between ecumenism and evangelization is fundamental. "Discord among Christians is the greatest obstacle to evangelization," said the Holy Father in March. And Jesus' dying wish for us was that we all be one (John 17:21) "so that the world may believe." If we are evangelizers, one of our goals each day should be to make some mark for Christian unity.

How do we do that? Everyone can pray for it. Everyone can offer it silently at the intentions of Mass -- in general and in particular ways. Everyone can strive for greater personal holiness -- drawing closer to the meeting point of all Christians, Jesus. Everyone can examine himself or herself for over-generalizing about other Christians.

They say, "Blood is thicker than water." But what if the blood is the blood of the Cross and the water is the water of Holy Baptism? Then both form a bond which eternally connects all Christians into a family. We can all hold our thoughts, words, and actions to the standard of utmost charity towards our brothers and sisters. All of us can learn more about them. All of us can build relationships. All of us can see the world differently in light of this bond.

There is much more we can do to make a difference. The Church has given us guidance and exhortation, and providence has given us the circumstances in our city and in our lives to make the unity -- albeit incomplete and imperfect--which we already share a living reality. In our region, one of the greatest opportunities for this is the presence of a wide range of Christian communities from all over the world, including the Greek Orthodox. Their Metropolis (like an archdiocese) is led by His Eminence, Metropolitan Methodios. Together, the cardinal and metropolitan -- building on their predecessors -- are continuing to actualize on the ground the intentions of the Holy Father and other Christian leaders to work toward unity.

That's what the joint letter of May 21 is about. It is a fruit of the realization on the local level of the progress made so far towards completing the remarkable unity we Orthodox and Catholics already share. The letter is rare -- something that happens perhaps once or twice a decade. It is significant in the way it links what we do with the Holy Father's trip and all that our Churches have done building up to it. It is yet another manifestation of communion between our local Church and the Church of Rome -- and communion is what it's all about in the quest for complete Christian unity.

The joint letter describes a little bit of our relationship between the metropolis and the archdiocese. There is much more than one short letter could contain. At midnight on this past Easter Eve at the Cathedral of the Metropolis the metropolitan gathered with his clergy and faithful for the Easter Vigil. With the church nearly dark and all holding unlit candles, the cardinal arrived from having concluded the Easter Vigil in our cathedral. The metropolitan gave him the Gospel to read, and together they proclaimed the Resurrection as light passed from candle to candle symbolizing the life of Christ which we all share.

Only full unity between us is enough. That is why Pope Francis with Eastern Catholic Patriarchs is going to pray with Ecumenical Patriarch Bartholomew and Armenian Christians and many other Christian representatives at the empty tomb from which that Easter light shines. Only full unity is true to the nature of the Triune God as communion. Only full unity obeys the will of Jesus, and therefore loves him. Only full unity is the goal set by the Magisterium. Only full unity honors the bond of our Baptism and eternal relation in Christ. Only full unity is coherent with the message of the Gospel of reconciliation. Only full unity empowers our compassion and unfetters our evangelization.

Take advantage of the opportunities to build Christian unity in your life. If you would like more ideas on how, contact the Office for Ecumenical and Interreligious Affairs, 617-746-5799.

Vito Nicastro, M.Div., Ph.D. is assistant director of the Office for Ecumenical and Interreligious Affairs of the Archdiocese of Boston.