70 Because, Venerable Brothers, the Sacrament of the Eucharist is a sign and cause of the unity of Christ's Mystical Body, and because it stirs up an active "ecclesial" spirit in those who are more fervent in their Eucharistic devotion, never stop urging your faithful, as they approach the Mystery of the Eucharist, to learn to embrace the Church's cause as their own, to pray to God without slackening, to offer themselves to God as an acceptable sacrifice for the peace and unity of the Church; so that all the sons of the Church may be united and feel united and there may be no divisions among them but rather unity of mind and intention, as the Apostle commands. (72) May all those who are not yet in perfect communion with the Catholic Church and who glory in the name of Christian despite their separation from her, come as soon as possible to share with us, through the help of God's grace, in that unity of faith and communion that Christ wanted to be the distinctive mark of His disciples.
Source: Mysterium Fidei (Vatican.va)