The raven has always been known as an intelligent bird, resourceful enough to save worthwhile items it will later use either as tools or to barter with. In Norse culture, ravens were revered for their cleverness. Vikings, for example, depended on them to help navigate their ships through unknown waters: when released from their cages, the ravens would either fly to nearby land or return to their ship if no land was in sight. And the god Odin is often depicted accompanied by his two ravens Huginn and Muninn, Norse symbols of Thought and Memory.
But the raven is also a carrion bird, so it came to be associated with the realm of the dead - in both good and bad ways. On the one hand, ravens have long been foreboding symbols of death, pestilence, disease and general misfortune. But by the same token, they are also seen as links between the living and the dead. Like angels, they are sometimes thought to be divine messengers, able to offer guidance by telling the future or revealing deep mysteries. That's why, as a spirit animal, the raven can bring positive things into one's life: guidance, knowledge, insight, and introspection.