CATECHISM OF THE CATHOLIC CHURCH
SECOND EDITION

Paragraphs 182–186

182 We believe all "that which is contained in the word of God, written or handed down, and which the Church proposes for belief as divinely revealed" (Paul VI, CPG § 20).
183 Faith is necessary for salvation. The Lord himself affirms: "He who believes and is baptized will be saved; but he who does not believe will be condemned" (Mk 16:16).
184 "Faith is a foretaste of the knowledge that will make us blessed in the life to come" (St. Thomas Aquinas. Comp. theol. 1, 2).
185 Whoever says "I believe" says "I pledge myself to what we believe." Communion in faith needs a common language of faith, normative for all and uniting all in the same confession of faith.
186 From the beginning, the apostolic Church expressed and handed on her faith in brief formula normative for all. But already very early on, the Church also wanted to gather the essential elements of her faith into organic and articulated summaries, intended especially for candidates for Baptism:

This synthesis of faith was not made to accord with human opinions, but rather what was of the greatest importance was gathered from all the Scriptures, to present the one teaching of the faith in its entirety. And just as the mustard seed contains a great number of branches in a tiny grain, so too this summary of faith encompassed in a few words the whole knowledge of the true religion contained in the Old and the New Testaments.