Her missionary activity doesn’t necessarily make her a member of the visible one universal Church,
Correct but the fact that she taught Scripture, the Gospel sraight from the Bible no doctrine does.
The early Church Father Origen, in one of his letters (A.D. 235), refers to the existence of private individuals who hold “false opinions” and make “ignorant assertions” about matters on faith by failing to understand the Scriptures on account of a feeble spiritual sense and a tendency to interpret them purely in a literal sense apart from the Apostolic Tradition of the Catholic Church and her teaching authority. Church doctrines have never been formed by initially gleaning the Scriptures and taking it from there. They originate from the sacred traditional beliefs of the Church as handed down from the Apostles and guided by the Holy Spirit. The New Testament itself is an inspired written work that acknowledges the sacred traditions of the Church and present them in literary form (cf.Lk 1:1-4). Thus Origen further asserts in his letter (First Principles, 4, 1:9) that the Scriptures can be properly interpreted as a means of doctrinal affirmation only by the episcopate of the Catholic Church which has legitimately succeeded the Apostles as guardians of the true faith.
Scripture is materially sufficient, but formally insufficient. There is much contained in the written word that is difficult for private individuals to grasp on their own initiative because of what remains to be implicitly revealed and unexplained. When Irenaeus invited those who had succumbed to the false teachings of the gnostic sects to be “nourished in the Lord’s Scriptures”, he wasn’t advocating sola Scriptura, as many Protestant apologists mistakenly maintain, but rather affirming that Scripture must be interpreted in light of Apostolic Tradition, from whence it has its source by the agency of the Holy Spirit, who inspired the authors of the sacred texts to write what they did for the benefit of future generations of a globally expanding church. The gnostics erred because they spurned the ecclesiastic traditions and the apostolic teaching authority of the Church, substituting these two pillars of truth for the Bible alone by rejecting them altogether and essentially putting their trust in themselves: the phenomenom of the competent soul, which has reappeared most starkly in contemporary Christian Fundamentalism. Put a loaded pistol in the hands of the wrong person, expect nothing but trouble if he misuses the firearm.
Like the gnostics of the 2nd century, Fundamentalists believe that they alone have been granted full access to the truth of our Lord’s word, that they’re connected with Jesus on an exclusive wavelength of the highest frequency and possess privileged information, having become a Church unto themselves, who are the ultimate authority in interpreting the Scriptures according to what they believe they have intuitively perceived through the infallible operation of the Holy Spirit after reading the Holy Book. Such circular reasoning is a mark of subjectivism, which has always plagued Protestantism since the Reformation as the source of its perpetual splintering. Martin Luther himself bemoaned this trend which he realized he started, for he actually believed what he doctrinally proposed, in accordance with his personal interpretation of the Scriptures, was true Christian dogma for the start of a new age in the Catholic Church and a reshaping of her traditional beliefs. Once he was excommunicated, it was his wish that every Catholic - clergy and laity alike - would follow him and accept his teachings under one umbrella. To preserve Christian untity we must, in the words of Origen, “cling to the standard of the heavenly Church of Jesus Christ according to the succesion of the Apostles.”