The law of hospitality in the oasis is the idea that any stranger entering the oasis must be given food and shelter during their stay in the oasis. The oasis is considered a safe-haven. Weapons are also forbidden in the oasis. It's in the oasis that Santiago searches for the Alchemist and is introduced to the elders who put forth quite a challenge for Santiago to fulfill.
The oasis is a beautiful area of the desert. There are many colorful tents and colors fill the scene. It serves as not only a literal contrast to the desert itself, but also as a metaphorical contrast to the "outside" world, the world of Santiago's quest to fulfill his personal legend. It's a respite from the rigors of the journey for Santiago and any other traveler who happens upon it.