Melchizedek was the King of Salem & priest of his God. There were several gods being worshiped at that time.
14 And when Abram heard that his brother was taken captive, he led forth his trained men, born in his house, three hundred and eighteen, and pursued as far as Dan.
15 And he divided himself against them by night, he and his servants, and smote them, and pursued them unto Hobah, which is on the left hand of Damascus.
16 And he brought back all the goods, and also brought back his brother Lot, and his goods, and the women also, and the people.
17 And the king of Sodom went out to meet him, after his return from the slaughter of Chedorlaomer and the kings that were with him, at the vale of Shaveh--the same is the King's Vale.
18 And Melchizedek king of Salem brought forth bread and wine; and he was priest of G-d the Most High.
19 And he blessed him, and said: 'Blessed be Abram of G-d Most High, Maker of heaven and earth;
20 and blessed be G-d the Most High, who hath delivered thine enemies into thy hand.' And he gave him a tenth of all.
** Notice how Melchizedek was the priest of God the most high.
** Notice how he blesses (or giving honor) to Abram of G-d Most High, MAKER OF HEAVEN AND EARTH.
**Maker of Heaven & Earth lets us know that there were 2 different gods being pointed out. He (Melchizedek) also gives Abram a tenth, Abram does not give him a tenth.