Chasidut zu Bereschit 18:5

Genesis 18,5. “for this is why your journey has brought you to the ‎house of your servant.” On the face of it, this is a very unusual ‎manner of extending an invitation to passing strangers to partake ‎of a meal with the host. The commentators explained that angels ‎are recipients of the largesse provided by G’d for the Jewish ‎people who have performed G’d’s commandments. In other ‎words, it was G’d Himself, Who took the butter, etc., described in ‎this verse, and served it to these strangers who were angels ‎garbed in human clothing. Avraham, personally, was not able to ‎perform his duties as an attentive host due to his not yet having ‎recovered from the effects of the circumcision. Under normal ‎circumstances, these men would have been denied his hospitality. ‎He therefore explains that due to his having fulfilled the ‎commandment of circumcision, they would in fact be partaking ‎of a meal provided by G’d Himself. They had been sent to him so ‎that he could take credit for hosting them.
We have to ‎elaborate somewhat on the tradition that Avraham had been ‎observing, voluntarily, all of the commandments that would later ‎on be found in the Torah. The only exception he had made was ‎the commandment of circumcision. In light of the fact that this ‎commandment was the cornerstone of G’d’s covenant with the ‎Jewish people, why would Avraham purposely have neglected to ‎perform this commandment until being told to observe it? ‎