Each year on the solemnity of Sts. Peter and Paul on June 29, the pope bestows on recently named metropolitan archbishops (those who oversee dioceses or archdioceses that are the largest in their ecclesiastical province) the pallium.
The pallium is a white scarf-like vestment that is worn over a bishop's (or pope's) chasuble and has been used by the Church since at least the 4th century.
They are made of wool from lambs that are presented on the feast of St. Agnes of Rome (January 21), whose name became associated with the Latin word for lamb (agnus). Two lambs are traditionally blessed by the pope on that day and then on Holy Thursday the sheep's wool is sheared.
On account of this association, it is symbolically connected to the idea of the bishop being a "shepherd" of his flock, caring for their needs.
A heavy burden
The symbolism goes even further, as the pallium has additional features, as the Office of Liturgical Celebrations explains:
It is decorated with six crosses of black silk, one on each end and four on the incurvature, and is decorated in front and on the back, with three pins made of gold and jewels (acicula)."
This might seem like a simple artistic choice, but it is meant to evoke a particular meaning.
The crosses recall the cross that Jesus bore on his shoulders, plus his five wounds. Additionally, the three pins symbolize the three nails that were driven into Jesus' hands and feet.
Black is also a deliberate choice, as it reminds the bishop of the need to "die to self" as part of his ministry. Sometimes the color red was used, and that too has a similar idea, recalling the blood that must be spilt in active ministry.
Pope Benedict XVI spoke about the meaning behind the pallium in his first homily as pope, saying, "The symbolism of the pallium is even more concrete: the lamb's wool is meant to represent the lost, sick, or weak sheep which the shepherd places on his shoulders and carries to the waters of life."
Archbishops who receive the pallium have much responsibility in the Church and should recall this symbolism whenever they wear the pallium.
It is both an invitation and a warning, reminding them that many souls are counting on their ministry.
