We continue with paragraph 8 of the Dogmatic Constitution on Divine Revelation.
8. And so the apostolic preaching, which is expressed in a special way in the inspired books, was to be preserved by an unending succession of preachers until the end of time. Therefore the Apostles, handing on what they themselves had received, warn the faithful to hold fast to the traditions which they have learned either by word of mouth or by letter (see 2 Thess. 2:15), and to fight in defense of the faith handed on once and for all (see Jude 1:3) (cf. Second Council of Nicea: Denzinger 303 (602); Fourth Council of Constance, session X, Canon 1: Denzinger 336 [650-652]). Now what was handed on by the Apostles includes everything which contributes toward the holiness of life and increase in faith of the peoples of God; and so the Church, in her teaching, life and worship, perpetuates and hands on to all generations all that she herself is, all that she believes.
This tradition which comes from the Apostles develop in the Church with the help of the Holy Spirit (cf. First Vatican Council, Dogmatic Constitution on the Catholic Faith, Chap. 4, “On Faith and Reason:” Denzinger 1800 ). For there is a growth in the understanding of the realities and the words which have been handed down. This happens through the contemplation and study made by believers, who treasure these things in their hearts (see Luke 2:19, 51) through a penetrating understanding of the spiritual realities which they experience, and through the preaching of those who have received through Episcopal succession the sure gift of truth. For as the centuries succeed one another, the Church constantly moves forward toward the fullness of divine truth until the words of God reach their complete fulfillment in her.
The words of the holy fathers witness to the presence of this living tradition, whose wealth is poured into the practice and life of the believing and praying Church. Through the same tradition the Church’s full canon of the sacred books is known, and the sacred writings themselves are more profoundly understood and unceasingly made active in her; and thus God, who spoke of old, uninterruptedly converses with the bride of His beloved Son; and the Holy Spirit, through whom the living voice of the Gospel resounds in the Church, and through her, in the world, leads unto all truth those who believe and makes the word of Christ dwell abundantly in them (see Col. 3:16).
Picking up from paragraph 7, this passage elaborates on the unfolding of revelation in time through the tradition of the Church. I recently came across an excellent analogy for the development of doctrine which compares it to the popular puzzle game Sudoku. Revelation is complete, but there is still room for an increase in understanding.