Hunting for the Right Words

Finding the correct word or words to express an idea is often a challenge for an author. There is an image, an idea and it needs to be expressed in as few syllables as possible. 
For example. 
A small child pours out the contents of his piggy bank to help his unemployed father. 
A grandmother with failing knees crawls up a set of stairs to bring her sick daughter a bowl of chicken soup. 
A small puppy lunges to its masters defense against a powerful dog.

There is something in the self-sacrifice of a character lacking in ability that stirs strong emotions in observers. The need to be useful, to serve others despite what their own infirmity might be is inspiring. But what do you call that reaction? The stirring of powerful emotion in the hearts of the observers? How does and author describe that dynamic?