Why do Matthew, Mark and Luke tell the same stories in the same words?

Because, most scholars think, the gospel writers used each other's texts. Matthew, Mark and Luke are called the synoptic Gospels because they share many of the same stories, often in the same order and sometimes in identical wording. By one count, 97.2 percent of the words in Mark have a parallel in Matthew and 88.4 percent in Luke. Explaining that overlap is called the synoptic problem.

The majority answer is Marcan priority: Mark, the shortest gospel, was written first, and Matthew and Luke each used it. But Matthew and Luke also share some two hundred verses that Mark lacks. In 1838 Christian Hermann Weisse proposed that they drew on a second, lost source made mostly of sayings of Jesus. It became known as Q, from the German Quelle, "source".

No one has ever found Q. No manuscript survives, and no ancient writer mentions it; even Jerome, who used the great library of Caesarea, says nothing of such a book. So a growing number of scholars drop Q and argue that Luke simply used Matthew, the Farrer hypothesis.

The question is famously stubborn. An international seminar of New Testament scholars worked on it for twelve years and, when it disbanded in 1982, admitted it had not reached agreement on a single issue. The two-source theory still has majority support, but one eminent scholar called the problem "practically insoluble". Note that this is a question about how texts were composed, which believers and sceptics can study alike.