Catechism of the Catholic Church §1561 — excerpt
The above considerations explain why the Eucharist celebrated by the bishop has a quite special significance as an expression of the Church gathered around the altar, with the one who represents Christ, the Good Shepherd and Head of his Church, presiding.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Also cites: SC 41 · LG 26