Hosting strangers in our homes and offering them food, and even lodging, is a primary Jewish duty. Years ago, travelers and other guests would frequent the dinner tables of observant Jews on Sabbaths and festivals. In fact, the shamash , or the sexton, of the synagogue would assign all poor guests to various private residences throughout the congregation for Shabbat and holiday dinners. I must emphasize that this mitzvah of hospitality applies not to close friends and family members, whom you would naturally invite. The point is to include those who might otherwise be overlooked and excluded,especially the poor and the needy.
Hospitality is a way of demonstrating our compassion.
It says that we know the heart of the stranger, because we were strangers for four centuries in the bondaged Egypt. Our paragon of hospitality is found in our Torah portion for this Sabbath. Sitting by his tent at the hottest time of the day, he sees three strangers approaching. At the time, he has no idea that they are people of distinction. They are actually God's messengers, announcing to him and Sarah, his wife, that they will soon become parents in their very advanced years.