The meaning of those two ravens is not 100% answered, yet. One possible explanation is as follows:

In the Norse shamanic tradition, Odin's ravens represent the powers of necromancy, clairvoyance and telepathy, and they were guides for the dead. This poem expresses the shaman's fear of his loss of magical powers. The Well of Remembrance by Ralph Metzner, Shambala, Boston, 1994

However, it is implied the name of one of the ravens is mistranslated:

it’s often claimed that Munin’s name means “Memory,” but for this to be so, it would have to be derived from minni, “memory,” rather than munr, “desire.” The latter, however, is by far the more parsimonious derivation; if the former were the case, we should expect Munin’s Old Norse name to have been something like “Minninn” rather than “Muninn.” Moreover, the above verse from the Grímnismál makes much more sense if Munin’s name means “Desire” rather than “Memory”. Norse Mythology for Smart People

Another possible explanation is the following, which is similar to first one:

Anthony Winterbourne connects Huginn and Muninn to the Norse concepts of the fylgja—a concept with three characteristics; shape-shifting abilities, good fortune, and the guardian spirit—and the hamingja—the ghostly double of a person that may appear in the form of an animal. Winterbourne states that “The shaman’s journey through the different parts of the cosmos is symbolized by the hamingja concept of the shape-shifting soul, and gains another symbolic dimension for the Norse soul in the account of Oðin’s ravens, Huginn and Muninn.” My Travels with Huggin and Munnin

However, Rudolf Simek has an entirely different point to make, saying that the names of the ravens were only used in later times: