In this chapter we see one of the reasons I believe that Abram was chosen by God to bless all the earth. If you will remember the story of Cain and Able, you will recall that when Cain slew Able and God asked him about it he asked “am I my brother's keeper?” In this chapter we find that Abram IS his brother's keeper and that pleases God very much as we shall see.  Am I my brother's keeper OR I am my brother's keeper; the difference between the two is huge.
God accepts anyone who comes to Him in truth but God chooses who He uses for a reason, not because they are perfect but because, among other things, they are just and courageous.
Vs. 1-12
Sodom is attacked and overcome, among the captives is Lot, Abram's nephew. In these chapters we see that wars of conquest have been around since the beginning and probably will be till the end. As James said in chapter 4 of his book:  1. From whence come wars and fightings among you? come they not hence, even of your lusts that war in your members? 2.  Ye lust, and have not: ye kill, and desire to have, and cannot obtain: ye fight and war, yet ye have not, because ye ask not.
You know if you think about it nothing REAL has changed in 6000 years, sure we have new inventions and greater knowledge of the universe and the world around us as well as greater knowledge about medicine and many other things but PEOPLE are the same and are motivated by the same things now as they were then. All our inventions only make us more efficient, not more wise and certainly not better people, only the transforming power of the Holy Spirit made available through our acceptance of Jesus in our hearts can do that and even then it is a battle.  
Before anyone thinks I am anti-war I am not, I hate war, I say though that no sane person wants war but no sane person avoids war at any cost either. In Revelations it says: “And I saw heaven opened, and behold a white horse; and he that sat upon him was called Faithful and True, and in righteousness he doth judge and make war.” Rev 19:11 so there is a time when it is justified. We do our best and God is our judge. In this case it was a war of conquest, a type which God can and has used to accomplish His plans, but is seldom justified. (Israel's conquest of the holy land being one exception)

Vs. 13-17
As soon as Abram finds out what happened he began preparing to intervene and successfully retrieves his nephew and everything else that was taken. At this point one might ask “how does Abram defeat all these kings with 318 people when all the kings of the valley couldn't do it with presumably many more people?” Well read on and you will see. In verse 17 we see that the king of Sodom comes to see Abram.

Vs. 18-20
“18. And Melchizedek king of Salem brought forth bread and wine: and he was the priest of the most high God.
19.  And he blessed him, and said, Blessed be Abram of the most high God, possessor of heaven and earth:
20.  And blessed be the most high God, which hath delivered thine enemies into thy hand. And he gave him tithes of all.”

This figure Melchizedek is the source of a lot of speculation but since I really haven't studied it enough to comment on him I will only note the following;
1. Salem is the same city as Jerusalem which was renamed after David conquered it. Interestingly it is one of the last areas to be conquered and occupied in all the land that God had given Abraham. Some of that land (as spelled out in Numbers 34) has yet to be conquered in my opinion.
2. Melchizedek was someone respected in the region, enough so that Abram gives him tithes.
3. He was both king of Salem and priest of the most high God and evidently widely known as such. No separation of church and state here!

Vs. 21- 24
The king of Sodom, who possibly was present when Melchizedek and Abram met offers to give Abram all the goods that he had recovered yet Abram had made an oath not to keep any of it so that none could say that they had made Abram rich. He would repeat this later though remember that he accepted gifts from the king of Egypt previously, perhaps Abram was learning that God was his source and putting it into practice.
Chapter 15