"Slaves no more, but brothers and sisters" is the title of the message Pope Francis will deliver for the 2015 World Day of Peace, the Pontifical Council for Justice and Peace stated Thursday.

"Slavery is a terrible open wound on the contemporary social body, a fatal running sore on the flesh of Christ," the pontifical council said in an Aug. 21 statement.

The World Day of Peace is observed annually on Jan. 1, and was initiated by Paul VI. It's celebration in 2015 will be the 48th iteration of the event.

Pope Francis chose the theme of slavery from a set of three proposed by the Pontifical Council for Justice and Peace, but himself added the reference to fraternity to the title.

This is in continuity with his message for this year's World Day of Peace, "Fraternity, the Foundation and Pathway to Peace."

And by choosing the theme of slavery, Pope Francis confirms his focus on human trafficking, which has surfaced throughout his pontificate.

"Many people think that slavery is a thing of the past. In fact, this social plague remains all too real in today's world," the statement of the Pontifical Council for Justice and Peace noted.

"Slavery deals a murderous blow to … fraternity, and so to peace as well. Peace can only exist when each human being recognizes every other person as a brother or sister with the same dignity."

The note anticipates some of the main issues with which the papal message will deal: human trafficking, trade in migrants and prostitutes, exploitation, slave labour, and the enslavement of women and children.

The note reads that "shamefully, individuals and groups around the world profit from this slavery. They take advantage of the world's many conflicts, of the economic crisis and of corruption in order to carry out their evil."

The pontifical council stressed that to effectively counter slavery, "the inviolable dignity of every person must be recognized above all … being children of God gives all human beings equal dignity as brothers and sisters."

"Fraternity requires us to reject any inequality which would allow one person to enslave another. It demands instead that we act everywhere with proximity and generosity, thus leading to liberation and inclusion for everyone."

In addition, achieving a civilization "based on the equal dignity of every person without discrimination" will require the commitment of the media, education, and culture to a society pledged to freedom and justice, the dicastery stated.

The message will be sent to the foreign ministers of all the world, and is an indication of the Holy See's diplomatic line throughout the year, the Pontifical Council for Justice and Peace noted. This year is the first time that slavery will be the theme of the day.

According to an official of the pontifical council who spoke to CNA, the 2015 message should be shorter than those of recent years.

Over time, the length of papal messages for World Days of Peace has ballooned: Paul VI's last, for 1978, was around 2,900 words; St. John Paul II's, for 2005, was 3,500; Benedict XVI's for 2013 was 3,800; and Pope Francis' message for 2014 was nearly 5,000 words.