The Catholics added to what the Jews considered scripture. It clearly says the oracles of God were entrusted to the Jews not to the Catholics. Besides, all the apostles were Jews.
>>Those teachings were recorded by the Apostles and Gospel writers, preserved by the Catholic Church<<
They were added to by the Catholic Church. The Catholic Church cannot prove that the apostles taught some of the things they teach. Paul clearly said anyone who teaches something they didn't should be considered accursed.
>>and transmitted both orally<<
The simply prove what they claim as "orally" was also taught by the apostles.
I must not be understanding you.
What was added? If you are speaking of the Septuagint, that was completed by around 130 BC.
I don’t know why you are hanging on this one line about oracles. It is completely out of context. I looked into the meaning of this particular verse, and found several authors indicating the discussion was about whether Jewish converts had an advantage with God. The answer was “no” and that all men are sinners (liars, etc.).
Are you saying that the Catholic Church added to the Epistles of Paul and Peter, as well as to the Gospel writers?
What does the Church teach the Apostles didn’t? Recall in John 20:30” Many other signs also did Jesus in the sight of his disciples, which are not written in this book.” Recall also, in John 21:25 “But there are also many other things which Jesus did, which if they were written every one, the world itself, I think, would not be able to contain the books that should be written.”
It seems Our Lord, in doing many other signs likely talked about those signs, and gave lessons. Luke 24:45 says after the Resurrection, “Then He opened their understanding, that they might understand Scripture.” Don’t you think the Apostles would have spread that understanding, despite it not be written?
St. Matthew recounts in 28:20 “...teaching them to observe all things whatsoever I have commanded you: and behold I am with you all days, even to the consummation of the world.”
So, each Gospel writer tells us Jesus taught and did more than was recorded. Would the earliest of Catholics (Ignatius of Antioch, in 107, is recorded to use the term Catholic Church, and disciple of St. John the Apostle) have learned these things, especially since it was before the completion of the Gospels? There are no other contemporary sources to contradict this.
These contemporaries of the Apostles, the first bishops, had works recorded, that transmitted what the Apostles taught, BEFORE, either the Gospels were completed, or the Canon of Scripture was closed.
One last thing, do you believe all that is written in the Gospels? One should, though their accounts of some incidents are somewhat different, and some events are not captured in all 4. Again, it was teaching of the Apostles, not recorded in the Bible, but recorded in the works of disciples of the Apostles, along with the Scriptures that were taught to the earliest Christians.