Catechism of the Catholic Church §1383 — excerpt
The altar, around which the Church is gathered in the celebration of the Eucharist, represents the two aspects of the same mystery: the altar of the sacrifice and the table of the Lord.
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: St. Ambrose, De Sacr. 5, 2, 7: PL 16, 447C · St. Ambrose, De Sacr. 4, 2, 7: PL 16, 437D · Roman Missal, EP I (Roman Canon) 96: Supplices te rogamus, omnipotens Deus: iube haec perferri per manus sancti Angeli tui in sublime altare tuum, in conspectu divinae maiestatis tuae: ut, quotquot ex hac altaris participatione sacrosanctum Filii Corpus · Sanguinem sumpserimus, omni benedictione caelesti · gratia repleamur