Characters
(singing) The sun'll come out tomorrow, so you gotta hang on till tomorrow, come what may. Tomorrow, tomorrow, I love ya, tomorrow, you're only a day away.
— Annie • Annie

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
This is a sung promise of hope: hang on, because the sun will come out tomorrow, and tomorrow is only a day away. The speaker sings to the future itself, treating it like a friend to love, and finds comfort in believing tomorrow will be better.
Context reviewed