What did archaeologists learn about the burial? Why is the burial important?

Because burial is part of the religious practices of a people, and once you understand their ritual practices, you can learn more about their beliefs.

Explanation:

A good example is mummification performed by the Egyptians. The process was made with care and attention to send the Pharao's body and his soul to the other world. When you learn the ritual, and especially the way the pyramids were built (and why), you can understand how Egyptians face death and how they prepare themselves for it.

Burials were and still are important for the humanity. Since they are tightly connected with religion, one should look for the answers there. Firstly, the ritual of burying a dead person was a symbolic journey from the world of the alive to the world of the dead. Grave was supposed to be the final place of resting of the dead person. And, of course, this was an act of respect to the deeds of the one who died.