The Talmud states (Shabbos 127a) that receiving and hosting guests is greater than greeting G-d. We learn this from Genesis 18:3, “Avraham said, ‘My L-rd, if I have found favor in Your eyes, please do not leave your servant’.” Avraham asked G-d to wait while he attends to his guests.
 
The Mitzvah of Hachnosas Orchim (receiving and hosting guests) consists of three parts: אכילה(food), שתיה(drink) and לויה(escorting the guest on the way). The acronym for these Mitzvos is אשל (Aleph, Shin, Lamed).
 
After Avraham fed his guests, it states in Genesis 18:16, "Avraham walked with them to escort them". The Rambam writes (Hilchos Aveil 14:1), "There is a mitzvah enacted by the Sages to visit the sick, to comfort the bereaved, to conduct a funeral for the dead, to marry off a bride and to escort guests as they are leaving."
 
The Rambam gives us a short list of five mitzvos that we are required to do for other people. If you would ask people to vote on which one is the most important mitzvah and which is the least important, what would they say? My guess would be that most people would say that escorting guests, the last mentioned, is the least important mitzvah.
 
But the Rambam writes in the very next halacha (14:2), "The reward for escorting guests is greater than all the rest. This is the legacy that our patriarch, Avraham, established." Thus Rambam lists this Mitzvah of escorting guests last because of the rule, “אחרון אחרון חביב” (saving the best for last).
 
But how could this be? You come into a hospital room. Your friend is lying there sick and pale. You visit him and you pray for him. You cheer him up. You've done a great mitzvah. You come to pay a shivah call. The bereaved has just lost a loved one, and he feels sad and depressed. You speak words of consolation that warm his heart. You make him feel better. You lift his spirits. It's a wonderful mitzvah. You arrange a funeral. You arrange a wedding. Terrific mitzvos. But what are you accomplishing when you escort your guest out of your house? He enjoyed his meal at your table. He is finished. He is going home. And you walk with him a short distance out of the house. What is so great about that? Why is that the greatest of these five mitzvos?
 
This is because when you escort a guest beyond your doorstep, you are showing him respect. You are giving him dignity. You are acknowledging that he is a somebody, and that he is deserving of your attention and concern. You are demonstrating that you enjoyed your guest’s company and would like to invite him back again. That is a critical need for people.
 
We can survive without food for a while. We can even survive without water for a while. We can walk in tattered clothes. We can endure all of this if we are treated with dignity and respect, as is befitting the Tzelem Elokim (The Divine image) that we are. That's why the Talmud says (Kesubos 111b) that it is a greater mitzvah to give a person a greeting with a smile than to give him a delicious milk desert. This is the legacy and heritage of Avraham Avinu.