Avraham receives the guests:
Avraham sat in the opening of the tent in the heat of the day when Hashem visited him [on the third day after his circumcision].
Why did Hashem visit Avraham?
Hashem visited our home for the sake of performing the mitzvah of Bikkur Cholim:
Who did Avraham advise with regarding the circumcision?
Avraham consulted with Aner, Eshkol, and Mamarei regarding the circumcision. It was specifically Mamarei who advised him to go ahead and perform the circumcision and therefore the verse states that the circumcision took place in the plains of Mamarei was one mainly responsible for the advice.
At what time in the day did God visit our?
It was at the fourth hour of the day.
What day of the year was the day of God’s visitation to our Avraham?
it was the 12th day of Tishrei
 Rabbienu Bechayh