Elevation of the Sacred Host at Mass.

This week dedicated to praying for the unity of Christians falls between a (former) feast of St Peter and the feast of the Conversion of St Paul. This shows that our unity as Christians is founded on the apostles and on the rock of Peter expressed today by communion with the Pope, his successor.
The Church has four ‘marks’ by which we can tell it is the true Church of Jesus Christ. We profess them in the Creed every week: the Church is one, holy, catholic and apostolic. The unity of the Church is expressed by a common faith (handed down from the apostles in scripture and tradition and taught by the Pope and the bishops in union with him), a common worship (centred on the celebration of the Holy Mass) and a common governance of the Church (under the Pope and the bishops in union with him).
We express this union in every Mass that is celebrated by praying for the Pope and the bishop in the Canon. The Eucharist is the sacrament of unity in the Church because all those who receive it are united together in Christ.