It really is the parable of the Good Samaritan blown into global proportions.
The other aspect of God’s grace shown by hospitality is the continuing sacrifices that a host makes for their guest throughout the Bible. Abram kills some of his flock and prepares the best wheat for dinner in Genesis 18 http://bible.us/Gen18.1.NET for the 3 guests that visit him on their way to Sodom.
Lot protects the guests from the townspeople even to the level of offering his own daughters to them when they want the guests thrown out his front door. http://bible.us/Gen19.8.NET
All of this (and there are many more events like this in the life of Elijah, David, etc.) points to God sending His son to pursue us, and then protecting us from the evil one by a great sacrifice on our behalf.