Abraham said: before I was circumcised, the passersby used to come to me. Do you mean to say that now, since I have been circumcised, they no longer come to me? The Holy One, blessed be He, said to him: before you were circumcised, uncircumcised human beings used to come to you; now I Myself in My glory am revealed to you. This is what is written, "And the LORD appeared to him in the plains of Mamre" (Genesis 18:1).
Once Abraham Was Circumcised God Appeared to Him in Person
Yalkut Shimoni on Torah 82:10
אָמַר אַבְרָהָם עַד שְׁלֹא מַלְתִּי הָיוּ הָעוֹבְרִים וְשָׁבִים בָּאִים אֶצְלִי, תֹּאמַר מִשֶׁמַּלְתִּי שֶׁאֵין בָּאִים אֶצְלִי, אָמַר לוֹ הַקָּדוֹשׁ בָּרוּךְ הוּא עַד שְׁלֹא מַלְתָּ הָיוּ בָּאִים בְּנֵי אָדָם עַרֵלִים אֶצְלְךָ, עַכְשָׁיו אֲנִי בִּכְבוֹדִי נִגְלָה עָלֶיךָ. הֲדָא הוּא דִכְתִיב וַיֵרָא אֵלָיו ה' בְּאֵלֹנֵי מַמְרֵא.