While attributed to ancient Jewish rabbinical literature, it is a controversial doctrine for many reasons. It is a fact - in the Masoretic text of the OT - that Shem survived well into the time of Abram / Abraham.
The Septuagint is more accurate and has Shem dead long before Abraham.
The Masoretic texts were altered by the Rabbis after the time of Christ.
Thank you for that gem on Melchizedek I have always been curious as to why Abraham gave a tithe to a guy he did not know but if he attended that academy for prophets as a child he already knew who he was...and the passing of the mantle to a different person other than family member is not totally alien to Jewish culture, Elijah had no genetic relationship to Elisha. It certainly is fascinating which is one of the reasons I love it! LEX