(blót)played a huge role in most of the rituals that are known about today, and communal feasting on the meat of sacrificed animals, [...] The purpose of these sacrifices was to ensure fertility and growth. However, sudden crises or transitions such as births, weddings and burials could also be the reason. In those times there was a clear distinction between private and public faith, and the rituals were thus tied either to the household and the individual or to the structures of society.
When their chieftain dies, his family ask his slave-girls and slave-boys, “Who among you will die with him?” and some of them reply, “I shall.” Having said this, it becomes incumbent upon the person and it is impossible ever to turn back. Should that person try to, he is not permitted to do so. It is usually slave-girls who make this offer. [...] I quizzed the interpreter about her actions and he said, “The first time they lifted her, she said, ‘Behold, I see my father and my mother.’ The second time she said, ‘Behold, I see all of my dead kindred, seated.’ The third time she said, ‘Behold, I see my master, seated in Paradise. Paradise is beautiful and verdant. He is accompanied by his men and his male- slaves. He summons me, so bring me to him.’” So they brought her to the ship and she removed two bracelets that she was wearing, handing them to the woman called the “Angel of Death,” the one who was to kill her.
Source: Ibn Fadlan and the Rusiyyah
Why was there a need to sacrifice slaves after their master's death? Didn't people at the time believe that a chieftain, being a person of high importance, would enter Valhalla? If so, why would a slave be allowed to enter Valhalla?