The Trinity or any other doctrine was never meant to be proven using the Bible alone. The apostles didn't convert the pagan world using the Bible alone. They preached with Divine authority ORALLY and their message was confirmed by signs following.
So why all of the wrangling about Scriptures that are of a fragmentary nature? They are incomplete without the accompanying ORAL tradition. They are not understandable without the living and constant witness of the magisterial voice of the Church.
BTW, according to the Bible Alone, WHAT is the pillar and ground of the truth? (For the answer, please see 2 Tim. 3:15)
