The word ambivalence means having mixed feelings or ideas about something or someone.
If I understand the sentence correct , it is saying....
We want to be happy for our mixed feelings about becoming better people"
We shouldn't close our hearts to the unfortunate. People that are unfortunate are people that have life harder than me and you. (poor people, homeless, orphans)
So , We shouldn't close our hearts to the unfortunate mean "we should be happy to help those people anytime"