A long time ago in a place far away, Abraham had been made promises. The Lord had come to him where he was and told him to leave his home and family and go to another place that would be identified for him later. The Lord promised him, "I will make you a great nation...."
Abraham made the move. A long time has passed. He's 99 years old. His wife Sarah who is 90 has not had a child, yet.
One day while Abraham is sitting at the entrance of his tent, he looks up and sees three visitors. He immediately offers them hospitality. He tells his wife Sarah to make some cakes with choice flour and he slaughters a tender calf so that they might have a good meal.
We have a picture of an obedient servant to the Lord. When he knows that it is the Lord speaking, he obeys. Moreover, when he doesn't recognize the Lord, he still is an hospitable as if he knew who his guests were.