Hospitality in ancient Hellenic was a complicated ritual within both the host and the guest has certain roles to fill and tasks to perform. Especially when someone unknown to the host came to the door, the ritual held great value. This ritual practice of hospitality was called 'xenia' (ξενία) and is described a lot in mythology. This, because any unknown traveler at the door could be a Theos or Theia in disguise or they could even be watched over by a Theos who would pass judgement on the host.
Hómēros, in the Odysseia, gives the following description of a guest being received at the door to the house; in this case by Athena, who is disguised as Mentes, as greeted by Telemachos, son of Odysseus.
"...Godlike Telemachus, sitting troubled among the suitors, imagining how his noble father might arrive from somewhere, throw the suitors from the palace, win honour and rule his own again, was first to see her. Thinking of it, sitting among the suitors, he saw Athene, and went straight to the doorway, ashamed a stranger should wait so long at the gates. Approaching her, he clasped her right hand, took her spear of bronze, and spoke to her winged words: ‘Welcome, stranger, here you will find hospitality, and after you have eaten you may tell us why you are here.’
At this, he led the way, and Pallas Athene followed. Once inside the high hall, he took the spear and set it in a polished rack by a tall pillar, with other spears that belonged to loyal Odysseus. He led Athene herself to a handsome, richly carved chair, spread a linen cloth over it, and seated her there with a footstool for her feet. He drew up on ornate stool for himself, as well, away from the Suitors, lest the stranger should shun the food, annoyed by the din, finding himself in a crowd of insolent men: and so he might ask news of his absent father. Next a maid brought water in a fine gold jug, and poured it over a silver basin, so they could rinse their hands: then drew up a polished table. The housekeeper silently brought them bread, and various delicacies, drawing liberally on her store. And a carver lifted plates of different meats, and set them down with gold cups beside them, while a steward, constantly walking by, poured the wine."
There are several things of interest to note in these passages; a guest should not have to wait to be greeted, they must always be accepted into the house and offered the best of everything, an inquiry as to the nature of the visit is delayed until the guest has eaten, recovered from the journey and sometimes--as found in other sources--has bathed and/or slept. Often, everything is set aside to help the guest with his or her quest because it was assumed no man or woman left their home unless they really had to.
Next to this, there are two other important rules concerning Xenia; the guest is expected to be courteous and not be a burden to the host and, and this is very important, the host must give the guest a parting gift--a xenion (ξεινήιον). The more valuable the gift, the better. In fact, Telemachos receives from Menelaus a cup made by Hēphaistos Himself:
"But stay here in the palace, till the eleventh or the twelfth day, and I will send you off with honours, and fine gifts, a shining chariot with a trio of horses, and a glorious cup with which to pour libations to the deathless gods, while remembering me all your days."
Mythology has a lot of examples of Theoi disguising themselves as beggars or undesirables. The host is judged on the hospitality offered. Good things befall those who treat guests with respect, very bad things befall those who do not. One of my favorite Hellenic myths shows this in great detail; it's the story of how Baucis and Philemon received some unexpected visitors. You can read a long version of the myth here but it comes down to this:
"Zeus and His son Hermes descended to earth to test the hospitality of the little town that is home to the elderly couple of Baucis and Philemon, who live in a run down hut a little ways away from the small, rural village. The Gods are dressed as simple travelers, weary from their long journey on foot. They knock on the doors of all of the houses in the village but find no one willing to open the door and take them in. With every house the Gods pass, the anger of the Gods rises, but before They punish this town for their despicable ways, They decide to test the last house in the village as well; the house of Baucis and Philemon.
It is Philemon who opens the door after the first knock and begs the travelers to enter. The hut is tiny and the two, who have been together for almost all of their long years, have not much to give. Still, the two bustle around the hut to repair enough stools for all to sit, to find enough food for all to eat and, as the night progresses, enough places for all to sleep. Neither Baucis nor Philemon realizes the true nature of their guests until they realize the small jug of wine has not run out, betraying the divinity of their guests.
Both Baucis and Philemon throw themselves down in front of the Gods, begging for forgiveness for such a sorry welcome but the Gods, who have not been offended in the least, beg them to rise and walk out with Them, to the top of the hill. There, Zeus turns to the village and floods the valley completely, killing all residents. He spares the hut that belongs to Baucis and Philemon and even transforms it into a temple. He then asks what favor the pair would want from the Gods, as they have truly deserved one. The pair asks to honor the Gods for their remaining eyars in the temple created below and ask that, when their dying day comes, that they may go together so they will never be without the other. This, the Gods grant happily."
With stories like this, it's easy to see why hospitality was so important in ancient Hellas, and holds a vital role in Hellenismos today. Not only do the Gods punish those who do not show proper Xenia, They reward those who do--handsomely, I might add.
One God in particular watches over guests and the practice of xenia; Zeus Xenios, an epithet of Zeus. It was to him, libations were poured when a guest arrived. Two example from the Odysseia; the first as Odysseus washes ashore Phaeacia and declares himself to Nausicaa, the second as he meets Nausicaa's father Alcinous.
"...With this she called to her lovely maids: ‘Stop, girls, why do you shun the sight of a man? Surely you don’t imagine he’s unfriendly? There will never be mortal man so contrary as to set hostile feet on Phaeacian land, for we are dear to the gods. We live far-off, over the turbulent sea, the remotest of races, and deal with no other peoples. This man must instead be some luckless wanderer, landed here. We must care for him, since all strangers and beggars come from Zeus, and even a little gift is welcome. So bring him food and drink, girls, and bathe him in the river wherever there’s shelter from the wind."
"With this he sat down in the hearth’s ashes, close to the fire, and all remained silent. At last one of the Phaeacian elders, noble Echeneus, eloquent and wise, spoke to them. Helpfully, he addressed the gathering, saying: ‘Come, Alcinous, it is not right and proper that a stranger should sit there in the ashes of the hearth, while we all hold back awaiting your lead. Raise the stranger to his feet, and seat him on a silver-embossed chair, and let the heralds mix the wine, so that we may pour libations to Zeus as well, who hurls the lightning and follows the footsteps of holy suppliants. And let the housekeeper feed him supper from her store.'"
In contemporary culture, hospitality has lost much of its meaning and practice. Gifts are brought for the host these days, refills are in the fridge, staying for dinner is only possible if you have and appointment, etc. Bringing back some of the old hospitality customs might not be a bad thing at all. It would sure bring us closer as a community and, really, it would be wonderful to knock on the door of a house when you're in need and know that you would receive all the help the host can possibly give.