Parshat Vayera 3

The Midrash Tanchuma (quoted in part by Rashi to Genesis 18; 1) explains why G-d appeared to Avraham in Alonei Mamre:
Avraham had three close friends, Aner, Eshkol and Mamre. When G-d told Avraham to circumcise himself he asked each of them for advice. Aner told him that he would endanger himself if the relatives of the kings came for revenge and would be unable to flee. Eshkol said to him that it was dangerous at his age to perform this operation. Mamre replied, “What are you asking for advice for? G-d has saved you from the fiery furnace into which you were thrown by Nimrod, and performed miracles for you and saved you from the four kings. Were it not for Him and his powers you would have been killed. G-d saved all of your 248 limbs and organs, and yet when He asks you to sacrifice a little bit of one part of your body you come to me for advice?” Because Mamre gave Avraham the advice G-d chose to reveal Himself to Avraham in his territory. This is why the Torah says “G-d appeared to [Avraham] in the fields of Mamre”.
Why did Avraham chose to ask advice, surely after all that he had been through and all the tests that he had faced he would not doubt G-d’s commands. And why did Avraham not follow the majority opinion to not circumcise himself. Aner and Eshkol’s advice seems as valid as Mamre’s.
Avraham and Sarah devoted themselves to bringing the message of monotheism to the world. Wherever they travelled they would gather people to them and show them the foolishness of idolatry, and the truth of a belief in one G-d. These people in turn would continue to teach others about G-d, and bring more people close to G-d. The person closest to Avraham was his servant Eliezer, and Avraham had assumed that he who would inherit him and continue with Avraham’s work.
To be able to make an impact on the world, Avraham needed to be preaching a universal message. Any religious beliefs or requirements that would set Avraham and his followers apart from the rest of society would minimise the number of people who would join the faith. Though Avraham was not afraid to set himself apart from the rest of society (he is called Ivri because he set himself on one bank of the river even though the whole world was on the other side), he thought that the future of monotheism was with those he could influence. He was therefore concerned to attract as many followers as possible.
However, G-d had other plans. G-d knew that Judaism would not be continued through those who had become attached to Avraham. They were more influenced by his personality than his beliefs, and without Avraham at the helm they gave up and disappeared from history. Despite all the followers that Avraham had gathered during his lifetime, when the Jews went down to Egypt, only Ya’akov and his immediate family remained.
Avraham underestimated the need for an heir to ensure the continuation of monotheism. He also failed to realise that it is through the uniqueness of the future Jewish nation that they will survive. When G-d told him to circumcise himself and his entire household, he didn’t question G-d’s commands. However he wanted to understand them. How would others react to Avraham making himself physically different than any other nation? Could he retain converts and allies if he alienated himself through circumcision? Therefore he first asked his three close friends for their advice.
Avraham would have performed G-d’s command regardless of the advice he received, which is why he didn’t follow the majority opinion. He wanted to gauge the response of others. Though Aner and Eshkol gave seemingly sensible advice, they showed their lack of faith in G-d. They were looking at the normal course of events, and didn’t realise that Avraham’s realtionship with G-d was beyond the natural cycle. Only Mamre understood that the whole religion of Avraham was based on continued miracles. Avraham perceived from Mamre’s advice that though many of the nations may choose not to understand the relationship of Avraham and his descendants with G-d, if they would look with an open mind they could come to terms with the uniqueness of the nation. Circumcision was a prerequisite for Yitzchak’s birth, because only once Avraham had himself shown to the world that Judaism is beyond the natural order, would G-d perform the miracle of giving him and Sarah a child.
It is the individuality and uniqueness of Judaism that have kept the nation alive for over 3000 years. Whenever the Jews tried to become like the surrounding nations they have grown weak and slowly disappeared. Only through the uniqueness symbolised by circumcision, and shown through the miraculous birth of Yitzchak, have they been able to remain a nation, and make the uniqueness of G-d known in the world.
The Malbim captures this idea in his commentary to the verse “Av Hamon Goyim” (17; 5) which is the meaning of the name Avraham: “Do not think that the nations will reject you becasue you have circumcised yourself. On the contrary, as a result of your distinction they will regard you as their guide and patriarch.”