Why does the Pasuk use the doubled expression, "If even a thread or shoe-lace; and if I take of anything that is yours"?
Rashi: "If even a thread or shoelace..." I shall withhold from the spoils; "... and if I take of anything that is yours" - [means,] I shall not take reward from your treasuries." 1
Seforno: Avraham was telling the King of Sedom under oath, that even if he wanted, he could not 2 return any of the spoils to him (even as much as a thread 3 ), since he had never taken it for himself in the first place. He would not take any gift from him either.
Why did Avraham refuse to accept the King of Sedom's offer to keep the spoils of war for himself?
Rashi (in Chulin, 89a): Because he did not want to benefit from stolen money.
Moshav Zekenim #1: One should not benefit from money of a Rasha who did not do anything good with his money.
Moshav Zekenim #2: Avraham wanted that people would attribute his wealth only to HaSh-m, who had promised to enrich him (12:2). 1
Mishnas R. Aharon (Vol. 3, p. 119): Even though the spoils were fully permitted through despair of the owners, and conquest in war, Avraham had the Midah of "Kol" - he has everything, and he cannot add to what he has through what is in another's hand.
Ohr Yechezkel, (Midos, p. 170): Avraham trusted that HaSh-m promised to make him rich directly, and not through others, for (taking from others) opposes the essence of a Ba'al Chesed.
Why was Avraham concerned that, if he accepted any gifts from the King of Sedom, the latter would claim that he had made him rich?
Rashi: Avraham's refusal was based on the fact that HaSh-m had promised him wealth, and he did not want the King of Sedom to override HaSh-m's promise. 1
Targum Yonasan: So that the King of Sedom should not then boast of what he had done.
Gur Aryeh: We cannot say that Avraham protested due to his own honor, rather, he was concerned for HaSh-m's honor.
The Gemara (Chulin 88b) states that in the merit of this statement, Avraham's descendants merited the Techeiles thread of the Tzitzis, and the straps (Retzu'os) of the Tefilin. Why specifically these two Mitzvos?
Maharal (Nesivos Olam, Nesiv Osher Ch. 1, p. 223): Avraham was able to say this due to his trait of contentment with that which was his (Histapekus). Such a person shows that he is complete, and not lacking. Tzitzis is a Mitzvah that applies directly on the body, and Tefilin on the head (representing the Nefesh); they are evidence of a person's completion.
QUESTIONS ON RASHI
Rashi writes: "I shall not take reward from your treasuries." Is this not obvious; if Avraham even returned even the spoils that were rightfully his (taken after Yi'ush)?
Gur Aryeh: The king of Sedom thought that perhaps Avraham refused to take of the spoils, because they could by identified as belonging to others, and he would be accused of having taken them against their owners' will. Monetary payment however, cannot be identified, and he thought that Avraham would accept it.
Rashi writes: "... for HaSh-m has [already] promised to make me wealthy, saying 'I shall bless you' (12:2)." What would be so bad if HaSh-m's promise was fulfilled in this manner? We find that Avraham did in fact accept gifts from Pharaoh?
Gur Aryeh: The king of Sedom did not give anything willingly. Also, that which came about through misfortune cannot be called "blessing." Pharaoh, however, gave in Avraham's honor (while the plague Pharaoh suffered was not a misfortune, but rather an atonement.) Refer to 12:13:4:5.