Lech Lecha 5772

Every day of our lives we recite the Shemoneh Esrei along with the first bracha of "Magen Avraham" (meaning Hashem is the Shield of Avraham). Why is it specifically Avraham that is mentioned? The Da'as Zekeinim of the Baalei Tosafos explain that the bracha is based on a pasuk in the parsha. Right after the war of the kings, Hashem tells Avraham not to be afraid, for He will protect Avraham. What was Avraham afraid of? The D"Z quote a Midrash Tanchuma that Avraham was afraid his number of merits decreased because he had killed the kings. Hashem then called to him saying, "Don't be afraid, you burned thorns in the vineyard, and I will protect you." Therefore, we say the Shield of Avraham because Hashem said this straight out only to Avraham.