Wow. Add this Apostolic Letter of Pope Paul VI -- Solemni Hac Liturgia -- to the list of documents from the era around Vatican II that people have just plum overlooked! (Another document on that list is Pope Bl. John XXIII's Veterum Sapientia, about the importance of the Latin language in the Church and the education thereof.)
It is an aggiornamento (bringing up-to-date) of the Nicene-Constantinopolitan Creed... in a good way. His Holiness expounds on the elements of the Creed, reinforcing the Catholic faith in a time of "disquiet which agitates certain modern quarters with regard to the faith", "in which so many certainties are being disputed". Without being "strictly speaking a dogmatic definition", it is a bold re-affirmation of so many elements of the Catholic faith.
This document should be required reading in every RCIA session around the world!
The Pope speaks of the Trinity and its Persons, Mary the Mother of God (specifically her perpetual virginity, Immaculate Conception, Assumption, and universal Motherhood), original sin, being reborn in the Holy Spirit, baptism, the Church of Jesus Christ founded on Peter and its four marks, the Word (in Scripture, Tradition, and Authority), the single Shepherd of the Church, the Holy Sacrifice of the Mass being the sacramental presentation of the Sacrifice of Calvary, the transubtantiation of the bread and wine into the Body and Blood of Jesus Christ, the temporal concern of the Church, purgatory, the communion of saints, and the Resurrection.
Blessed be God Thrice Holy. Amen.