In Genesis 14:17-24 Abraham meets Malkizedek the king of Salem after he defeats the kings of the east, and we find (NIV):
17 After Abram returned from defeating Kedorlaomer and the kings allied with him, the king of Sodom came out to meet him in the Valley of Shaveh (that is, the King’s Valley).
18 Then Melchizedek king of Salem brought out bread and wine. He was priest of God Most High, 19 and he blessed Abram, saying,
“Blessed be Abram by God Most High [El Elyon], Creator of heaven and earth. 20 And praise be to God Most High, who delivered your enemies into your hand.” Then Abram gave him a tenth of everything.
21 The king of Sodom said to Abram, “Give me the people and keep the goods for yourself.”
22 But Abram said to the king of Sodom, “With raised hand I have sworn an oath to the Lord, God Most High [Yahweh El Elyon], Creator of heaven and earth, 23 that I will accept nothing belonging to you, not even a thread or the strap of a sandal, so that you will never be able to say, ‘I made Abram rich.’ 24 I will accept nothing but what my men have eaten and the share that belongs to the men who went with me—to Aner, Eshkol and Mamre. Let them have their share.”
I find this passage extremely disturbing, and I think that traditional scholars have not given these verses enough attention. El Elyon was a famous Canaanite deity and Malkizedek is undoubtedly referring to him in verse 17. Abraham seems here to accept the blessing of Malkizedek the priest of El Elyon and even pays him tithes. This refutes the common traditional belief that Abraham was a monotheist.
But even more puzzling is verse 22 where Abraham identifies El Elyon with Yahweh! Did Abraham forsake the gods of his homeland in Mesopotamia only to embrace the brutish gods of Canaan? Granted that Abraham was not a monotheist and was probably not as harsh with polytheism as the Mosaic religion was, but why would Abraham identify his own deity (Yahweh or El Shaddai) with a foreign Canaanite deity? Furthermore, if Abraham believed that there isn’t much of a difference between Yahweh and El Elyon and possibly even the Mesopotamian gods, and that they are all a manifestation of the same god, what makes the Abrahamic religion any different from the ancient Near Eastern religions, and what’s so unique about it? And if there was nothing unique about the Abrahamic religion then why would Moses even identify his own religion with that of the Patriarchs as he constantly identifies Yahweh the monotheistic god with his ancestors and calls him “the god of Abraham, Isaac and Jacob”?
So what I’m trying to figure out here is, what was the nature of the Abrahamic religion (as the above verses may reveal), and how similar was it to Mosaic religion? Was it polytheistic or monotheistic? If polytheistic, what was so unique about it and how was it different from the Mesopotamian religions of his homeland? Of course any good answer will have to take into account the identification of Yahweh with El Elyon in the Abrahamic worldview and offer some explanation.
I'm looking for well written scholarly answers, and not just poor unread speculations.