Catechism of the Catholic Church
“The Eucharist and the unity of Christians.
Before the greatness of this mystery St. Augustine exclaims, ‘O sacrament of devotion! O sign of unity! O bond of charity!’ The more painful the experience of the divisions in the Church which break the common participation in the table of the Lord, the more urgent are our prayers to the Lord that the time of complete unity among all who believe in him may return.”
Source: Catechism of the Catholic Church #1398