What do Christians mean when they say the Bible is true?

"Every Scripture is God-breathed and profitable for teaching, for reproof, for correction, and for instruction in righteousness, that each person who belongs to God may be complete, thoroughly equipped for every good work."

The sentence is about what scripture is for. It is a claim about origin and about use, and it makes no statement about error, genre or history. The translation quoted here even footnotes a second rendering of its opening, “Every writing inspired by God is”, under which the verse says that every inspired writing is profitable and not that every writing is inspired. Whatever a tradition builds on it, the building is not in the verse.

The Second Vatican Council put it this way: the books of scripture must be acknowledged as "teaching solidly, faithfully and without error that truth which God wanted put into sacred writings for the sake of salvation".

The same document instructs the reader to attend to literary forms, since "truth is set forth and expressed differently in texts which are variously historical, prophetic, poetic, or of other forms of discourse".

The Westminster Confession, written in the 1640s and still a standard of Presbyterian churches, speaks of the "infallible truth and divine authority" of scripture. It also says "the infallible rule of interpretation of Scripture is the Scripture itself", and that the supreme judge of religious controversy "can be no other but the Holy Spirit speaking in the Scripture".

That answers a different question: not what kind of sentences these are, but who decides what they mean. Dei Verbum answers it too, and differently: its rules for reading scripture are "subject finally to the judgment of the Church". Arguments about inerrancy between these traditions are often arguments about the second question conducted in the words of the first.

Matthew has Judas throw the silver into the sanctuary and hang himself, and the chief priests buy the potter’s field with it. Acts has Judas obtain a field "with the reward for his wickedness" and, "falling headlong", burst open, and the field is called the field of blood.

Two accounts, one field, different buyers and different deaths. Every account of what it means to call this book true has to be able to say something about a passage like this, and the answers differ.

Read one way, "for the sake of salvation" restricts the guarantee to what the text teaches for salvation and leaves its incidental history and cosmology as the furniture of its age. Read another way it describes the purpose of the whole without limiting what within it is true.

That sentence was argued over in the drafting: the fourth draft removed the word “any” before “error” and added “saving” to qualify “truth”, which is what caused the controversy. Paul VI had “saving” taken out, which let the phrase about salvation in; the commentator Aloys Grillmeier says the change was meant to avoid implying limited inerrancy, and then reads the clause as limiting it anyway. Fifty years on, the article cited here reports that debate still exists about what the council fathers intended. Worth knowing before anybody cites the clause as settling the matter.

A parable is not a lie. An ancient biography that arranges its material by theme is not a forgery, and the tradition Papias recorded about Mark says as much: he wrote "accurately, though not in order", and "committed no error" in doing so. A psalm saying the earth is founded and cannot be moved is not a geological claim.

Accounts far apart on inerrancy agree that genre matters: Dei Verbum says so, and so does the Chicago Statement on Biblical Inerrancy. They disagree about where the line runs, particularly in the passages where the genre is exactly what is in dispute.

Few of these texts say anything about their own inspiration, and none says that what it has written is without error. Jeremiah is told to write in a scroll all the words God has spoken to him. The Revelation to John says God gave it, and threatens anyone who adds to its words or takes from them. Paul tells one church that what he writes is the Lord’s command. Luke says he investigated and wrote an orderly account, which is a historian’s preface and not a claim to be without error.

The doctrines are later readings of a collection whose authors said little about how it was to be read.

At one end, as the Chicago Statement puts it, scripture is without error in history and science as well as in faith, and discrepancies not yet resolved do not count against it. In the middle, the text is without error in what it teaches for salvation and human in everything else. At the other end is the view the Chicago Statement denies: that the Bible is "merely a witness to revelation", or "only becomes revelation in encounter".

All three are held by people who read the same book carefully and pray to the same God. That is not a scandal, it is the actual situation, and a reader who knows it can tell which claim is being made.

Whether the book is true in any of these senses is outside what evidence settles. What is inside it: what the documents say, which passages the disagreement turns on, and which tradition holds which position. All of that is checkable, and this question is filed as uncertain rather than unknown for exactly that reason.