There are people who easily identify with another individual, who relate to what the other is experiencing. They can usually also sympathize with any animal, with each beetle, with each sparrow, and be happy with whatever happens around them, or be sad together with the people they encounter who are sad. Notice how often it arises in life especially at a certain age, that a young person can be elated one moment and suddenly the next moment be intensely and extremely miserable. Some people will then say this is senseless, that it is neither here nor there! These two sorts of people exist. Of course, these qualities will be developed to a greater or lesser extent in particular cases, it may not at all be so strongly present, but the tendency will nonetheless be there.
Now the spiritual researcher considers such manifestations in the world and then comes to the following conclusion: Musical people are the ones who in a previous life found it easy to make the transition from happiness to sorrow … from sorrow to happiness, who went along easily with everything. This quality metamorphoses into the ability to be inwardly mobile and the aptitude in the inner life for rhythmic variation that generates the musical soul. By contrast, human beings who passed life by obtusely in a former life will not be musical in the next life.
Source (German): Rudolf Steiner – GA 169 – Weltwesen und Ichheit – Berlin, July 18, 1916 (page 154-155)
Translated by Nesta Carsten-Krüger