Answer:
The mockingbird symbolizes life that should be preserved for the nonmaterial value it provides people through its singing.
Step-by-step explanation:
Based on the excerpt, the mockingbird symbolizes the value of life that should be preserved even if the value it gives is non-material but the value it gives is aesthetic because it gives joy to people that listen to it when it sings.
"Mockingbirds don't do one thing but make music for us to enjoy." Here, we see that the mockingbird has no other function but to sing songs that is pleasing to the ear because that is its sole purpose.
"They don't do one thing but sing their hearts out for us." further shows the value of joy it brings as it sings its heart out just for the pleasure of others.