We are taught that Hashem made the weather very hot so that Avraham Avinu would be able to recuperate from his Brit Mila without disturbances.
Avraham was disappointed as he wanted to fulfill the Mitzva of הכנסת אורחים, welcoming guests. Hashem complied by sending the angels in the form of men so that he could do this Mitzva.
We also learn an important aspect of welcoming guests in the way he sent them off at the end of their visit.
The Torah says, אברהם הולך עמם לשלחם, that he went with them in order to send them off. From here we learn that when our guests leave, we should at least walk them to the door. Even better, we should walk them out of the house for a short distance.
Often, this is not such an easy Mitzva to fulfill. It is our task to make our visitors feel at home, welcome, and wanted. This sets the tone for the type of homes we have. And, an open and warm feeling, brings Kedusha to the home. When there is Kedusha, the Shechina is able to rest in such a home.
Avraham Avinu taught us not only the importance of הכנסת אורחים, but also how to do it.