This never ceases to amaze me!
A person can put there total faith in a book, but they have not chosen to objectively explore the book from a scholarly or historical perspective, they just believe everything it says, because that is what they were taught. Yet, on the other hand, these same people, will complete a myriad of psychological gymnastics, to discredit the work of science, even though science develops testable and empirical evidence to back it's claims. This is the king of double standards and hypocrisy.
Regarding Matthew, no Matthew did not write the gospel that has his name on it. In fact, NT scholars agree, Matthew, Mark, Luke and John, were not written by any of the four names attached to them, but were actually penned by ANONYMOUS authors who wrote the gospels in Greek and Jesus' followers spoke Aramaic and were also mostly illiterate. They were also written 30-70 years after Jesus died, contained no verifiable eye witness accounts and have tons of errors and contradictions. The originals are lost and we only have copies of copies starting around 200AD.
Why is it relevant? Are you serious? You put all your faith in this book and ignore objective evidence from science when it disagrees with your book and you ask why is it relevant to examine the credibility of the book that causes you to ignore reality?