When is a beggar a god?

In traditions around the world we see the same mythic trope of a god disguised as a beggar so that he can test mortals. Very often this is based on a moral that one should uphold the ancient tradition of honouring the guest in one's home. The myths usually show the god, who can be Zeus, Shiva, or Odin, punishing the mortals who fail to show them proper hospitality when they visit. What lessons can pagans learn from these myths

Art 

Baucis and Philemon by Ryan Murray

The Chandala by Christopher Steininger

Sources

Primary:

Atharvaveda
Heimskringla
Homer, The Odyssey
Ovid, Metamorphoses
Orchard, A., (trans) The Elder Edda (2011)
The Rigveda
Sturluson, S., The Prose Edda
Togail Bruidne Dá Derga
Vidyaranya Swami, Shankara Digvijaya

Secondary:
von Glinski, M. L., Simile and Identity in Ovid's Metamorphoses
Murnaghan, S., Disguise and Recognition in the Odyssey