Our Mishna on Amud Beis discusses a scenario where a person makes a vow to not benefit from the uncircumcised. He is permitted to even benefit from Jews who were unable to circumcise themselves, and forbidden even to gentiles who did circumcise.  Furthermore, the opposite holds true as well.  If one makes an oath to refuse benefit from those who are circumcised, he is forbidden to all Jews, even those who are uncircumcised, and permitted to all gentiles, even those who are circumcised.

On a pashut peshat level, this halakha reflects a function of vernacular and idiom.  Such as one may refer to a person as white, based on race, even if he or she has meditarranean dark skin and may be darker than light colored persons who are ethnically and racially African American.  Language use does not always correspond with what might be the technical word.  However, this halakha also hints at a deeper idea.  The physical manifestation of something is not the same as the spiritual truth of the matter.  A person may be circumcised but not have reached the spiritual goal of the covenant that circumcision represents, and vice versa. The Torah uses the metaphor of being uncircumcised to mean an occlusion or lack of spiritual sensitivity, as perhaps the Torah sentiment wants us to have in regard to two of the most sensitive of organs, the heart and the reproductive organ (see Devarim 10:16).

Pri Tzaddik (Vayechi 17) discusses this idea.  He wonders why we make Havdala on wine, as what is the celebration?  It is one thing to welcome Shabbos and Yom Tov with festive drinking, but why celebrate the loss of Shabbos and Yom Tov? He answers that wisdom is built on discernment.  The joy and ability to appreciate Shabbos also comes from the ability to discern between the mundane and holy.  It is hard to appreciate and enjoy vacations unless it is in the context of a life filled with meaningful, challenging work. Havdala celebrates Shabbos by ending it. This is why being circumcised is not merely a physical act, but it is the tip of the iceberg in recognizing and accepting the spiritual role and responsibility of a religious person.  He marks the most sensitive aspects of himself with a reminder of God, body and heart.