The story about Avraham and Malkitzedek (Melchizedek in English translations) is not just exceptionally brief but also oddly placed within the story of the war of kings. After Avraham rescued the captured kings, the king of Sedom comes to thank him. But then the story shifts to Malkitzedek as follows (Gen. 14:18-20):
Then Melchizedek king of Salem brought out bread and wine; he was the priest of God Most High. And he blessed him and said: "Blessed be Abram of God Most High, Possessor of heaven and earth; And blessed be God Most High, Who has delivered your enemies into your hand." And he gave him a tithe of all.Click here to read moreAfterwards, the story returns to the king of Sedom. The narrative shift is jarring and classical biblical critics (e.g. Gunkel and Westerman) attributed it to a late interpolation from one biblical source into a narrative from a different source. The redactor evidently made a sloppy insertion that interrupts the story.
However, Prof. Nechama Leibowitz (New Studies in Bereshit, pp. 130-135) saw this differently. Without mentioning the critics, she addressed this interruption by quoting and explaining commentaries that sought to show that the Malkitzedek story advanced and enhanced the story about the king of Sedom story.
Both R. Yitzchak Abarbanel and R. Chaim Ibn Atar (the latter in his Or Ha-Chaim commentary) suggest that the exchange between Avraham and Malkitzedek shed light on the actions of the king of Sedom. Abarbanel asks what would possess the king of Sedom, right after being saved in battle by Avraham, to ask him for what amounts to a gift -- the captives from the war who were now slaves? Abarbanel answers that normally he would not but after seeing Avraham's generosity with Malkitzedek, the king of Sedom (correctly) surmised that Avraham might agree to such a request.
R. Chaim Ibn Atar takes a different approach. He sees Malkitzedek as a foil for the king of Sedom. Malkitzedek, who has no reason to be grateful to Avraham, generously approached him with food and drink after the battle. The king of Sedom, however, who had just been saved by Avraham, comes to him with a request rather than a gift. This shows the wickedness of the king of Sedom and foreshadows his city's later destruction due to its inhabitants' evil ways.
Nechama offers two other commentarial approaches to this story, which I will not summarize here (see Rashbam and Ramban, or Nechama's book).
Gordon Wenham (Word Biblical Commentary, vol. 1 pp. 305-307) adds a more textual basis to the claim that the Malkitzedek story is part of the larger unit. He points out that Malkitzedek's blessing of Avraham presupposes the immediately preceding story of the war. His "bringing out" (hotzi) seems to contrast the king of Sedom's "going out" (va-yeitzei) in verses 8 and 17. Similarly, in Avraham's final speech to the king of Sedom, he refers to "Lord, God Most High, the Possessor of heaven and earth" which is clearly a reference to Malkitzedek's words to Avraham. Wenham also points out that verse 17, part of the battle of the kings, ends with the word "melekh" and the next verse begins with "u-malkitzedek", which seems to be a verbal link between the verses.
Overall, there are both literary and linguistic reasons to see the Malkitzedek story as part of the larger unit and not as a clumsy interpolation.