The Tanach frequently tells us that somebody's name was changed, by God or people (Abraham, Sarah, Jacob, Joseph, Jethro, etc.), for a stated reason. But the Sages added that some latter-day biblical characters were the same as earlier ones: Keturah was Hagar, Melchizedek was Shem, Ethan haEzrachi was Abraham, etc.). If this is intended as factual, why wasn't it stated in Tanach? If these are intended as parables, what is the lesson?
Is this matter discussed anywhere?