Doorstep is one of the most sacred places in Serbian houses because it is believed that the dead ancestors gather under the doorstep stone. There are indications that Serbs (some of them anyway) used to bury their dead under the doorstep, where they would "protect the entrance into the house" from evil spirits.
So why did Serbs invite wolves to the feast in the same way they invited the dead to the feast?
Serbs venerated their ancestors. They believed that all that is good and bad comes from happy or unhappy ancestors. So it was extremely important to keep them happy, which usually meant entertained, well fed and well watered. This is why no major Serbian celebration could pass without the ancestors being invited to join. And Christmas in particular, being the biggest celebration in Serbian calendar, had to be celebrated together with the ancestors.
Now Serbs believed in Father Sky (Sun) and Mother Earth. They believed that they actually descended from these "deities". They particularly considered Dabog (Sky, Sun god) to be their forefather.
At the same time wolf was the totem animal of the Serbs, their animal twin. The belief that wolf was Serbian animal twin was manifested in many folk customs. For instance when a child was born, the custom in Serbian villages was for the father to open the house door, stand on the doorstep, and announce the birth of a son by shouting: "Rodila vučica vuka!" (A she-wolf just gave birth to a wolf cub!). A mother would announce its wolf nature to her child by singing it a lullaby which started with "Nini sine, vuče i bauče, vučica te u gori rodila" (Sleep my son, my wolf, a she-wolf gave birth to you in a mountain). A newborn baby was pulled through a wolf jaw to protect it from evil, illness and demons...In that way Dabog, the supreme god of the Serbs, the archetypal ancestor of the Serbs, who was also called the Wolf Shepherd, was giving his blessing to his new descendant. Amulets made from various parts of wolf body were used to protect people from various dangers including devil himself. The name Vuk (Wolf) is a very common Serbian name and it is believed that it protects the person from evil.
It was even believed that Serbs turn to wolves when they die.
Vampire, a dead body which gets out of the grave attacks people and sucks their blood is by Serbs also called vukodlak (werewolf).
In Montenegro and Hercegovina, Serbs simply called vampire "wolf". Serbian Kuči tribe from Montenegro believed that every vampire after a while turns into a wolf. The reason why vampire is seen as a wolf is because Dabog, the Wolf Shepherd, is not just the Sun (Sky) god, but also the good of the underworld, the good of the dead. Which is why his animal, wolf, a chthonic animal itself, is seen as a natural metamorphosis for the dead. Werewolf (Vampire) is the link between the world of the living and the world of the dead, as he is both dead and alive...
So this is why the same ritual invitation to the feast was performed for both the ancestors and the wolves.
In some parts of Serbia, the Christmas feast for wolves was laid on a crossroads and wolves were called to come and "take theirs and leave mine". The man who brought the food for wolves had to run home without turning.
Crossroads are one of the favourite gathering places of the dead. The "not turning while going home" rule is also applied to the family coming back from the graveyard after burying someone. Here again we see the link between the wolves and the dead...