To learn is to accrue knowledge, and to be learned spiritually is to have acquired knowledge through study. Dreams are a way for us to link with other levels of consciousness and acquire knowledge.
Psychological / emotional perspective: As we gather experience we learn more, and dreams can be a way of internalizing what we have learned. As a child learns more of the world in which he or she exists, dreams become a way of dealing with everyday experience.
Material aspects: When life is stressful we are able to learn methods of coping through dreams, not just through interpreting images but also by practising different behaviour through techniques like lucid dreaming. When we find ourselves in a learning situation in dreams, we should perhaps look at how these lessons can be applied in everyday life. You might also like to consult the entries for education, teacher and school.