"How do you know that the Book of Esther is the inspired Word of God and belongs in the canon of Scripture?"
This is a question I often ask Protestants. The Protestant literally has no way to prove that the book of Esther is inspired by God and belongs in the Bible. It is never quoted in the New Testament. It never mentions the word "God" in its pages. We don't know who wrote it. Even the first century Jews could not agree on its place as Scripture.
I sometimes also ask, "How do you know that the Book of Third John is the inspired Word of God and belongs in the Bible?" It doesn't claim to be written by an apostolic author and its authority was doubted by many early Christians.
The Catholic Christian has the comfort of knowing that the Holy Spirit can lead the Church to make infallible statements. Thus, the Bible is an infallible collection of infallible books.
However, the Protestant must follow the line that R.C. Sproul often gives: The Bible is a fallible collection of infallible books.
The Protestant can never give a reason for why he believes that Esther or 3 John belong in the canon of Scripture. Calvin said the books of Scripture attest to their own divine origin. But this begs the question? Attests to whom? What if someone reads a book of the Bible (let's take James for example) and after reading it thinks that it is merely an epistle of straw and contrary to the Gospel of Christ. Or what if someone reads the Shepherd of Hermes and concludes that it has the character of Scripture? Who gets to decide which books do and don't attest to their own divine origin?
The only sure way to solve the riddle is to appeal to the authority of the Catholic Church to infallibly determine matters of faith. However, if a Protestant does appeal to the Church in order to assure himself that he has an infallible collection of infallible books, he has to ask himself: "But what if the Catholic Church made other infallible statements?" And at this point, the Protestant begins to become a Catholic...
Are there any Protestants out there who feel that they can solve the problem without appealing to the infallible nature of the Catholic Church?