There are very few things more important than the basic pillars of Hellenismos. There are also few things harder to grasp. As such, getting questions about katharmos or, as in this case, kharis is not odd to me. This question came through Tumblr. I am going to recycle bits and pieces from older post for this reply.

"Helloo! I haven't been able to find the answer to this question and i really really would like that someone answer..! Did everyone believe in/practice kharis in ancient greece? Like was it common knowledge that a reciprocal relationship with the gods was the right kind or something? Thank you!!"

One of the most important practices within Hellenismos and ancient Hellenic orthopraxy is kharis (xάρις). Kharis is--to give an incredibly limited definition--the act of giving to the Gods so They might give something in return. It's religious reciprocity. It's also so much more.

Kharis is an important word. It means everything from beauty to joy, delight, kindness, good will, grace, favor, benefit, boon, charm, attraction, appeal, elegance, gracefulness, pleasure, cheerfulness, wit, gratitude, thankfulness and gratification. It's the name of a Goddess as well; the Goddess of Grace and Beauty. This seems to complicate matters, but it actually ties in pretty well.

When we, in Hellenismos, petition the Gods for aid, we always do so with an offering. This offering can be incense, a libation, a food offering or anything else. It must be something tangible. Good thoughts and intentions don't count. This offering is given freely, joyfully, with pleasure, out of respect and love for the Gods. We ask what we feel we need--sometimes that's a new job, sometimes just a vague sentiment like honour and prosperity to the household--and never expect to be granted this request. Petitions aren't bribery. We give to the Gods and should They feel inclined to grand us our request, we thank Them by offering to Them again, to which the Gods might respond, to which we will sacrifice, and so on. This circular practice of voluntary giving is called kharis.

Kharis is one of the pillars of Hellenismos, together with xenia and katharmos. Those who practiced kharis properly in ancient Hellas were seen as humble, grateful and good people in general. Kharis is the base of a good few words we use to describe related acts and characteristics to this day; charisma, for instance, and charity. To word it differently; kharis represents your reputation with a specific Deity.

Building a relationship with the Theoi was vital for the ancient Hellenes and it's vital in Hellenismos today. It's the foundation of daily practice, of the large-scale festivals of old, of Xenia, katharmos and the whole of Hellenismos. You can't practice Hellenismos without striving for a reciprocal relationship with the Gods.

Did everyone believe in the practice of kharis...? Well, no one will ever be able to answer that question, but I can tell you that from what we have found out about their society, the huge majority of the ancient Hellenes did, in fact, practice their religion this way. The Theoi were seen as people, as powerful persons who could interfere in your life either positively or negatively. Keeping Them happy was of major importance. It was not just the right thing to do, it was the vital thing to do; it was an extension of xenia--ritual hospitality--linked to Theoxenia. It was a way of living that extended to the Gods, and in reverse, extended from the Gods to humanity.

One of my favourite Hellenic myths shows the link between kharis and xenia in great detail, and also shows that the ancient Hellenes were very aware of the way they related to the Theoi; 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 travellers, 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 travellers 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 favour the pair would want from the Gods, as they have truly deserved one. The pair asks to honour the Gods for their remaining years 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."
This is how the ancient Hellenes saw religious reciprocity, and their relation to the Gods; it mattered greatly, and truly was a cornerstone of their life--and it should be ours as well.