Catechism of the Catholic Church: 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.” 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.
The CCC teaches that there will not be any new “public revelation”, meaning new Divine Revelation (which includes Sacred Tradition and Sacred Scripture). However, the Magisterium can teach seemingly new doctrines, which were always implicit in Sacred Tradition or Sacred Scripture. As time passes, the Church gradually increases Her understanding of Divine Revelation. Examples of this include the Immaculate Conception and the Assumption of Mary, as well as the path of salvation for non-Christians.
There will be “no new public revelation” before Christ Returns in his “glorious manifestation.” That is an interesting phrasing. My view, which is a minority opinion, is that Christ will return twice, once in a “glorious manifestation” at the end of the second part of the tribulation, and again, centuries later, for the general Resurrection. The teaching that there will be no new public revelation explicitly states a limit to that exclusion, the limit being what I would call the time of Christ’s first return. So, it is possible — this is not a dogma or doctrine, but merely a permissible opinion — it is possible that, when Christ returns at the end of the tribulation, He will teach and this teaching will be written down (Scripture) and He will again give the example of His own life and behavior (Tradition), so that both Sacred Tradition and Sacred Scripture will be augmented at that time. Thus, there may be a third Testament added to the Old Testament and the New Testament after the tribulation.
Sacred Tradition is divided into the Traditions of the Old Covenant and of the New Covenant. And Sacred Scripture is also divided into two parts, the Old and the New. So when Christ returns, each will be completed with a third part, which is a reflection of the Most Holy Trinity.
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