There is a difference between apostolic doctrine and true doctrine. This is because the apostles upon occasion taught error.
The apostles taught certain things that are provably false. Some of these are commonly categorized as "cultural" teachings no longer applying today. But there is no hint the apostles thought of these as cultural.
Also, they allowed Greek philosophy to color their thinking. Such wrong ideas as the body is bad.
They also strongly emphasized topics of interest to Jews such that whole books and letters discuss whether Jewish law has been abrogated.
Our authority for knowing truth depends on apostolic teaching. We have no other choice than to accept their teaching; after all, they learned it from Jesus himself. But we need to discover the things they added or changed, and reject these.
Here are things the apostles taught; some are true, some are not true ...
- Shun wicked Christians, and apparently there were many.
- The purpose of marriage it to avoid sin for those who are too weak to do so otherwise. Not a very high opinion of marriage.
- That Christians should not do such horrible wicked things. The teaching should be that these are not really Christians at all. Sadly, this kind of thinking pervaded the Church when the bishops were these doing such horrible wicked things.
- The apostles were aware their teachings were not always from God but were their own opinions.
- That Greek philosophy was true in many respects.
- Natural law, that various social customs and traditions are true because everyone (in that culture) knows them to be true.
- Jewish ideas about ritualistic cleanliness are true for all cultures and all times.
- Marriage is a distraction from the relationship with Jesus and interferes. Thus, time spent enjoying or serving your spouse and children is not time spent with God.
- Christians should not practice idolatry. This doesn't apply to us today, certainly not to Christians except perhaps those in a culture still practicing voodoo, shamanism, witchcraft, sorcery, trance channeling, or other kinds of spiritual practices.
- The Eucharist.