The Catechism paragraphs today deal with Divine Revelation revealed through Christ, the fact that there will be no further public revelation, the development of doctrines, and the nature of private revelation.

III. Christ Jesus -- "Mediator and Fullness of All Revelation"25

God has said everything in his Word

65 "In many and various ways God spoke of old to our fathers by the prophets, but in these last days he has spoken to us by a Son."26 Christ, the Son of God made man, is the Father's one, perfect and unsurpassable Word. In him he has said everything; there will be no other word than this one. St. John of the Cross, among others, commented strikingly on Hebrews 1:1-2:

In giving us his Son, his only Word (for he possesses no other), he spoke everything to us at once in this sole Word - and he has no more to say. . . because what he spoke before to the prophets in parts, he has now spoken all at once by giving us the All Who is His Son. Any person questioning God or desiring some vision or revelation would be guilty not only of foolish behaviour but also of offending him, by not fixing his eyes entirely upon Christ and by living with the desire for some other novelty.27

There will be no further Revelation

66 "The Christian economy, therefore, since it is the new and definitive Covenant, will never pass away; and no new public revelation is to be expected before the glorious manifestation of our Lord Jesus Christ."28 Yet even if Revelation is already complete, it has not been made completely explicit; it remains for Christian faith gradually to grasp its full significance over the course of the centuries.

67 Throughout the ages, there have been so-called "private" revelations, some of which have been recognized by the authority of the Church. They do not belong, however, to the deposit of faith. It is not their role to improve or complete Christ's definitive Revelation, but to help live more fully by it in a certain period of history. Guided by the Magisterium of the Church, the sensus fidelium knows how to discern and welcome in these revelations whatever constitutes an authentic call of Christ or his saints to the Church.

Christian faith cannot accept "revelations" that claim to surpass or correct the Revelation of which Christ is the fulfilment, as is the case in certain nonChristian religions and also in certain recent sects which base themselves on such "revelations".

IN BRIEF

73 God has revealed himself fully by sending his own Son, in whom he has established his covenant for ever. the Son is his Father's definitive Word; so there will be no further Revelation after him.

The Dogmatic Constitution Dei Verbum expounds upon the nature of Divine Revelation revealed through Jesus Christ:

4. Then, after speaking in many and varied ways through the prophets, "now at last in these days God has spoken to us in His Son" (Heb. 1:1-2). For He sent His Son, the eternal Word, who enlightens all men, so that He might dwell among men and tell them of the innermost being of God (see John 1:1-18). Jesus Christ, therefore, the Word made flesh, was sent as "a man to men." (3) He "speaks the words of God" (John 3;34), and completes the work of salvation which His Father gave Him to do (see John 5:36; John 17:4). To see Jesus is to see His Father (John 14:9). For this reason Jesus perfected revelation by fulfilling it through his whole work of making Himself present and manifesting Himself: through His words and deeds, His signs and wonders, but especially through His death and glorious resurrection from the dead and final sending of the Spirit of truth. Moreover He confirmed with divine testimony what revelation proclaimed, that God is with us to free us from the darkness of sin and death, and to raise us up to life eternal.

The Christian dispensation, therefore, as the new and definitive covenant, will never pass away and we now await no further new public revelation before the glorious manifestation of our Lord Jesus Christ (see 1 Tim. 6:14 and Tit. 2:13).

St. Vincent of Lerins expounds on the development of doctrine in the Catholic Church giving us a beautiful analogy about its growth without alteration:

[54] "But someone will say perhaps, 'Shall there, then, be no progress in Christ's Church?' Certainly; all possible progress. For what being is there, so envious of men, so full of hatred to God, who would seek to forbid it? Yet on condition that it be real progress, not alteration of the faith. For progress requires that the subject be enlarged in itself, alternation, that it be transformed into something else. The intelligence, then, the knowledge, the wisdom, as well of individuals as of all, as well of one man as of the whole Church, ought, in the course of ages and centuries, to increase and make much and vigorous progress; but yet only in its own kind; that is to say, in the same doctrine, in the same sense, and in the same meaning.

[55] The growth of religion in the soul must be analogous to the growth of the body, which, though in process of years it is developed and attains its full size, yet remains still the same. There is a wide difference between the flower of youth and the maturity of age; yet they who were once young are still the same now that they have become old, insomuch that though the stature and outward form of the individual are changed, yet his nature is one and the same, his person is one and the same. An infant's limbs are small, a young man's large, yet the infant and the young man are the same. Men when full grown have the same number of joints that they had when children; and if there be any to which mature age has given birth, these were already present in embryo, so that nothing new is produced in them when old which was not already latent in them when children. This, then, is undoubtedly a true and legitimate rule of progress, this the established and most beautiful order of growth, that mature age ever develops in the man those parts and forms which the wisdom of the Creator had already framed beforehand in the infant. Whereas, if the human form were changed into some shape belonging to another kind, or at any rate, if the number of its limbs were increased or diminished, the result would be that the whole body would become either a wreck or a monster, or, at the least, would be impaired and enfeebled.

[56] In like manner, it behooves Christian doctrine to follow the same laws of progress, so as to be consolidated by years, enlarged by time, refined by age, and yet, withal, to continue uncorrupt and unadulterated, complete and perfect in all the measurement of its parts, and so to speak, in all its proper members and senses, admitting no change, no waste of its distinctive property, no variation in its limits.

-St. Vincent of Lerins, “Commonitory” Ch 23

The Dogmatic Constitution Lumen Gentium comments on private revelation and its judgment:

It is not only through the sacraments and the ministries of the Church that the Holy Spirit sanctifies and leads the people of God and enriches it with virtues, but, "allotting his gifts to everyone according as He wills,(114) He distributes special graces among the faithful of every rank. By these gifts He makes them fit and ready to undertake the various tasks and offices which contribute toward the renewal and building up of the Church, according to the words of the Apostle: "The manifestation of the Spirit is given to everyone for profit".(115) These charisms, whether they be the more outstanding or the more simple and widely diffused, are to be received with thanksgiving and consolation for they are perfectly suited to and useful for the needs of the Church. Extraordinary gifts are not to be sought after, nor are the fruits of apostolic labor to be presumptuously expected from their use; but judgment as to their genuinity and proper use belongs to those who are appointed leaders in the Church, to whose special competence it belongs, not indeed to extinguish the Spirit, but to test all things and hold fast to that which is good.(116)

Footnotes

25 DV 2.
26 ⇒ Heb 1:1-2
27 St. John of the Cross, the Ascent of Mount Carmel 2, 22, 3-5 in The Collected Works of St. John of the Cross, tr. K. Kavanaugh OCD and O. Rodriguez OCD (Washington DC: Institute of Carmelite Studies, 1979), 179-180: LH, Advent, week 2, Monday, OR.
28 DV 4; cf. ⇒ I Tim 6:14; ⇒ Titus 2:13