The Holy Father Benedict XVI has written a message for the day focusing on the theme of "One human family," the text of which follows (with my emphases):
Dear Brothers and Sisters,
The World Day of Migrants and Refugees offers the whole Church an opportunity to reflect on a theme linked to the growing phenomenon of migration, to pray that hearts may open to Christian welcome and to the effort to increase in the world justice and charity, pillars on which to build an authentic and lasting peace. "As I have loved you, so you also should love one another" (Jn 13:34), is the invitation that the Lord forcefully addresses to us and renews us constantly: if the Father calls us to be beloved children in his dearly beloved Son, he also calls us to recognize each other as brothers and sisters in Christ.
This profound link between all human beings is the origin of the theme that I have chosen for our reflection this year: "One human family", one family of brothers and sisters in societies that are becoming ever more multiethnic and intercultural, where also people of various religions are urged to take part in dialogue, so that a serene and fruitful coexistence with respect for legitimate differences may be found. The Second Vatican Council affirms that "All peoples are one community and have one origin, because God caused the whole human race to dwell on the face of the earth (cf. Acts 17:26); they also have one final end, God" (Message for the World Day of Peace, 2008, 1). "His providence, His manifestations of goodness, His saving design extend to all men" (Declaration Nostra aetate, 1). Thus, "We do not live alongside one another purely by chance; all of us are progressing along a common path as men and women, and thus as brothers and sisters" (Message for the World Day of Peace, 2008, 6).
The road is the same, that of life, but the situations that we pass through on this route are different: many people have to face the difficult experience of migration in its various forms: internal or international, permanent or seasonal, economic or political, voluntary or forced. In various cases the departure from their Country is motivated by different forms of persecution, so that escape becomes necessary. Moreover, the phenomenon of globalization itself, characteristic of our epoch, is not only a social and economic process, but also entails "humanity itself [that] is becoming increasingly interconnected", crossing geographical and cultural boundaries. In this regard, the Church does not cease to recall that the deep sense of this epochal process and its fundamental ethical criterion are given by the unity of the human family and its development towards what is good (cf. Benedict XVI, Encyclical Caritas in veritate, 42). All, therefore, belong to one family, migrants and the local populations that welcome them, and all have the same right to enjoy the goods of the earth whose destination is universal, as the social doctrine of the Church teaches. It is here that solidarity and sharing are founded.
"In an increasingly globalized society, the common good and the effort to obtain it cannot fail to assume the dimensions of the whole human family, that is to say, the community of peoples and nations, in such a way as to shape the earthly city in unity and peace, rendering it to some degree an anticipation and a prefiguration of the undivided city of God" (Benedict XVI, Encyclical Caritas in veritate, 7). This is also the perspective with which to look at the reality of migration. In fact, as the Servant of God Paul VI formerly noted, "the weakening of brotherly ties between individuals and nations" (Encyclical Populorum progressio, 66), is a profound cause of underdevelopment and – we may add – has a major impact on the migration phenomenon. Human brotherhood is the, at times surprising, experience of a relationship that unites, of a profound bond with the other, different from me, based on the simple fact of being human beings. Assumed and lived responsibly, it fosters a life of communion and sharing with all and in particular with migrants; it supports the gift of self to others, for their good, for the good of all, in the local, national and world political communities.
Venerable John Paul II, on the occasion of this same Day celebrated in 2001, emphasized that "[the universal common good] includes the whole family of peoples, beyond every nationalistic egoism. The right to emigrate must be considered in this context. The Church recognizes this right in every human person, in its dual aspect of the possibility to leave one’s country and the possibility to enter another country to look for better conditions of life" (Message for World Day of Migration 2001, 3; cf. John XXIII, Encyclical Mater et Magistra, 30; Paul VI, Encyclical Octogesima adveniens, 17). At the same time, States have the right to regulate migration flows and to defend their own frontiers, always guaranteeing the respect due to the dignity of each and every human person. Immigrants, moreover, have the duty to integrate into the host Country, respecting its laws and its national identity. "The challenge is to combine the welcome due to every human being, especially when in need, with a reckoning of what is necessary for both the local inhabitants and the new arrivals to live a dignified and peaceful life" (World Day of Peace 2001, 13).
In this context, the presence of the Church, as the People of God journeying through history among all the other peoples, is a source of trust and hope. Indeed the Church is "in Christ like a sacrament or as a sign and instrument both of a very closely knit union with God and of the unity of the whole human race" (Second Vatican Ecumenical Council, Dogmatic Constitution Lumen gentium, 1); and through the action within her of the Holy Spirit, "the effort to establish a universal brotherhood is not a hopeless one" (Idem, Pastoral Constitution Gaudium et spes, 38). It is the Holy Eucharist in particular that constitutes, in the heart of the Church, an inexhaustible source of communion for the whole of humanity. It is thanks to this that the People of God includes "every nation, race, people, and tongue" (Rev 7:9), not with a sort of sacred power but with the superior service of charity. In fact the exercise of charity, especially for the poorest and weakest, is the criterion that proves the authenticity of the Eucharistic celebration (cf. John Paul II, Apostolic Letter Mane nobiscum Domine, 28).
The situation of refugees and of the other forced migrants, who are an important part of the migration phenomenon, should be specifically considered in the light of the theme "One human family". For these people who flee from violence and persecution the International Community has taken on precise commitments. Respect of their rights, as well as the legitimate concern for security and social coherence, foster a stable and harmonious coexistence.
Also in the case of those who are forced to migrate, solidarity is nourished by the "reserve" of love that is born from considering ourselves a single human family and, for the Catholic faithful, members of the Mystical Body of Christ: in fact we find ourselves depending on each other, all responsible for our brothers and sisters in humanity and, for those who believe, in the faith. As I have already had the opportunity to say, "Welcoming refugees and giving them hospitality is for everyone an imperative gesture of human solidarity, so that they may not feel isolated because of intolerance and disinterest" (General Audience, 20 June 2007: Insegnamenti II, 1 , 1158). This means that those who are forced to leave their homes or their country will be helped to find a place where they may live in peace and safety, where they may work and take on the rights and duties that exist in the Country that welcomes them, contributing to the common good and without forgetting the religious dimension of life.
Lastly, I would like to address a special thought, again accompanied by prayer, to the foreign and international students who are also a growing reality within the great migration phenomenon. This, as well, is a socially important category with a view to their return, as future leaders, to their Countries of origin. They constitute cultural and economic "bridges" between these Countries and the host Countries, and all this goes precisely in the direction of forming "one human family". This is the conviction that must support the commitment to foreign students and must accompany attention to their practical problems, such as financial difficulties or the hardship of feeling alone in facing a very different social and university context, as well as the difficulties of integration. In this regard, I would like to recall that "to belong to a university community… is to stand at the crossroads of the cultures that have formed the modern world" (John Paul II, To the Bishops of the United States of America of the Ecclesiastical Provinces of Chicago, Indianapolis and Milwaukee on their ad limina visit, 30 May 1998, 6: Insegnamenti XXI, 1  1116). At school and at university the culture of the new generations is formed: their capacity to see humanity as a family called to be united in diversity largely depends on these institutions.
Dear brothers and sisters, the world of migrants is vast and diversified. It knows wonderful and promising experiences, as well as, unfortunately, so many others that are tragic and unworthy of the human being and of societies that claim to be civil. For the Church this reality constitutes an eloquent sign of our times which further highlights humanity’s vocation to form one family, and, at the same time, the difficulties which, instead of uniting it, divide it and tear it apart. Let us not lose hope and let us together pray God, the Father of all, to help us – each in the first person – to be men and women capable of brotherly relationships and, at the social, political and institutional levels, so that understanding and reciprocal esteem among peoples and cultures may increase. With these hopes, as I invoke the intercession of Mary Most Holy, Stella Maris, I cordially impart the Apostolic Blessing to all and, especially, to migrants and refugees and to everyone who works in this important field.
From Castel Gandolfo, 27 September 2010