The expression “the consummation of the world” [in Matt 28:20] means the end of the world; “all days” means constantly, i.e., without any interruption, always. Therefore, Christ will be with the teaching-body which He established in His Apostles always and to the end of the world. Therefore, this same teaching-body will remain always and to the end of the world. But this would not be true unless the teaching-body were also perpetual and unchangeable, at least in its substantials. The teaching-body in its doctrines is unchangeable, for it cannot reject any doctrine of Christ; nor explain any doctrine in a sense contradictory to that already attributed to it; nor can any public relation be added which is altogether new. For
(a) If the teaching-body ever rejected any of Christ’s doctrines, it could err, and we have proved that it cannot err.
(b) If the teaching-body explained a doctrine in contradictory senses, it would have to reject one of these senses and admit its error.
(c) If the teaching-body added any new revelation to Christ’s doctrine, then this new revelation would be a truth of the Christian religion. But Christ promised: “But when, the Spirit of truth, is come he will teach you all truth” (John XVI, 13), and this certainly means that every truth of the Christian religion was entrusted to the Apostles. This, too, is the way they understood the promise, for e.g., Paul urges Timothy to guard the deposit of faith and to avoid all novelties (I Tim. VI, 20, 21; Galatians I, 6 to 9). And from the very beginning of Christ’s Church, it was an axiom among the foremost teachers that after the Apostles there would be no new public revelations. (Francis X. Doyle, Defense of the Catholic Church: Combined with a Study of the Life of Christ Based on the Gospels [1927; repr., Pekin, Ind.: Refuge of Sinners Publishing, Inc., 2022], 203)
The Holy Spirit always watches that the teaching-body does not make a mistake, and directs the teaching-body if it should be about to make a mistake. If, for instance, a false doctrine is about to be taught, the Holy Spirit would prevent it. Or if there is hesitation in the minds of the teachers as to what Christ taught, the Holy Spirit would excite clear and distinct ideas and true judgments on the matter, and suggest words and phrases which would convey the true doctrines accurately.
If the Holy Spirit did not continually watch, He would not assist, and the Apostles could err. And while, ordinarily, this watchfulness would suffice when matters are proceeding properly; still, since the teaching body of itself is an organization of weak human beings open to error, the Holy Spirit must at times effectively direct the teachers either by preventing the error, or by suggesting the true doctrine of Christ.
With such watchfulness and directions on the part of the Holy Spirit, the teaching-body can never make a mistake in teaching Christ’s doctrines. (Francis X. Doyle, Defense of the Catholic Church: Combined with a Study of the Life of Christ Based on the Gospels [1927; repr., Pekin, Ind.: Refuge of Sinners Publishing, Inc., 2022], 171)