A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
gen 14:1WAR. (Gen. 14:1-24)
And it came to pass--This chapter presents Abram in the unexpected character of a warrior. The occasion was this: The king of Sodom and the kings of the adjoining cities, after having been tributaries for twelve years to the king of Elam, combined to throw off his yoke. To chastise their rebellion, as he deemed it, Chedorlaomer, with the aid of three allies, invaded the territories of the refractory princes, defeated them in a pitched battle where the nature of the ground favored his army (Gen 14:10), and hastened in triumph on his homeward march, with a large amount of captives and booty, though merely a stranger.
gen 14:12they took Lot . . . and his goods, and departed--How would the conscience of that young man now upbraid him for his selfish folly and ingratitude in withdrawing from his kind and pious relative! Whenever we go out of the path of duty, we put ourselves away from God's protection, and cannot expect that the choice we make will be for our lasting good.
gen 14:13there came one that had escaped--Abram might have excused himself from taking any active concern in his "brother," that is, nephew, who little deserved that he should incur trouble or danger on his account. But Abram, far from rendering evil for evil, resolved to take immediate measures for the rescue of Lot.
gen 14:14And when Abram heard that his brother was taken captive, he armed his trained servants--domestic slaves, such as are common in Eastern countries still and are considered and treated as members of the family. If Abram could spare three hundred and eighteen slaves and leave a sufficient number to take care of the flocks, what a large establishment he must have had.
gen 14:15he divided himself . . . by night--This war between the petty princes of ancient Canaan is exactly the same as the frays and skirmishes between Arab chiefs in the present day. When a defeated party resolves to pursue the enemy, they wait till they are fast asleep; then, as they have no idea of posting sentinels, they rush upon them from different directions, strike down the tent poles--if there is any fight at all, it is the fray of a tumultuous mob--a panic commonly ensues, and the whole contest is ended with little or no loss on either side.
gen 14:18Melchizedek--This victory conferred a public benefit on that part of the country; and Abram, on his return, was treated with high respect and consideration, particularly by the king of Sodom and Melchizedek, who seems to have been one of the few native princes, if not the only one, who knew and worshipped, "the most high God," whom Abram served. This king who was a type of the Saviour (Heb 7:1), came to bless God for the victory which had been won, and in the name of God to bless Abram, by whose arms it had been achieved--a pious acknowledgment which we should imitate on succeeding in any lawful enterprise.
gen 14:20he gave him tithes of all--Here is an evidence of Abram's piety, as well as of his valor; for it was to a priest or official mediator between God and him that Abram gave a tenth of the spoil--a token of his gratitude and in honor of a divine ordinance (Pro 3:9).
gen 14:21the king of Sodom said . . . Give me the persons--According to the war customs still existing among the Arab tribes, Abram might have retained the recovered goods, and his right was acknowledged by the king of Sodom. But with honest pride, and a generosity unknown in that part of the world, he replied with strong phraseology common to the East, "I have lifted up mine hand" [that is, I have sworn] unto the Lord that I will not take from a thread even to a sandal-thong, and that that I will not take any thing that [is] thine, lest thou shouldst say, I have made Abram rich" [Gen 14:22-23].