In Parshat Vayera, Avraham has a few very distinguished guests, God and three angles. The Midrash tells us that Hashem came to visit Avraham who was sitting. It then raises the obvious question: Later, Avraham got up and rushed to serve the three angels, why didn't Avraham act in the same manner for Hashem?
The Midrash offers a few explanations, one stressing a very important lesson. When Hashem came to Avraham's home, Avraham did want to stand, as the proper host would. However, Hashem told Avraham to sit because everything in the world belongs to God, and, therefore, Avraham was His guest!
When the three angels arrived shortly thereafter, Avraham said to Hashem that he must stand to welcome the guests, for, according to them, he is their host. Avraham then proceeds to serve his guests, just as Hashem came to comfort Avraham.
From this scene in Avraham's life we learn two things. Firstly, we must always remember that, whatever we own, truly belongs to Hashem. Secondly, we must learn from Hashem and Avraham that it is important to treat our guests with respect, even if we are more powerful or rich than them. With this in mind, we can strive to be as modest as Avraham Avinu, and perhaps come a little closer to living Bitzelem Elokim.