So how do we learn about THOSE things? Apostolic Tradition. After all, the New Testament, as a book, didn't get put together until 420 A.D. And THOSE books were judged to be worthy and accurate by the Catholic bishops, the ROMAN Catholic bishops in Rome.
There is no line in Scripture that says that Scripture is the SOLE source of our teaching, but then, sola scriptura,is an invention of excommunicated Catholic priest, Doctor Father Martin Luther.
Father Luther did dump seven of the OT books (Tobias, Baruch, Judith, Wisdom, Ecclesiatics I and II, Macabees, seven chapters of the book of Esther, AND 66 verses of Daniel 3) and WANTED to dump the letter of St. James but his followers talked him into putting the letter of St. James BACK into "his" (his words not mine) New Testament.
I had an OLD friend (Reared Baptist, changed to Presbyterian because the Baptist church is her town (where she lived in as an adult) was not....well, not what she and her family wanted, read an excerpt from the Book of Wisdom at my husband's funeral. She called and said "Book of What?" We still laugh about that.
No, we don't learn from Apostolic Tradition. The early church fathers HAD no Apostolic Traditions. If you read their writtings they frequently used the inspired scriptures. When they veered off the path was normally when they interject their thoughts or opinions into something. That's not to say that we can't learn from others but things must be verified through scripture.
I've heard this "There is no line is Scripture that says the Scripture is the SOLE source of our teaching..." before, frequently from Catholics. This is a grave mistake. The early CHURCH fathers distinguish the difference between INSPIRED writing and UNINSPIRED writing. They called the INSPIRED writing the Bible. So what is really being said is that "We no longer believe the Scriptures to be solely the inspired word of God." This is completely against the teachings of the first 400 years of the Church.
Father Luther dumped the seven OT books because they were not acceptable to the early Church Fathers as inspired teachings-not because it was a whim of his.
And, currently, I'm a Baptist going to a Presbyterian church simply because I prefer a confessional church (one where we actually confess our sins). I have yet to hear them read from the Book of Wisdom. Where your friend went is most likely is the liberal branch of the Presbyterians. This should say something.