"The kindness of strangers did a lot to bring back my faith in humanity." If it still doesn't make sense, please let me know. :)

Here are a few more. "The kindness of strangers had restored my faith in humanity." "The kindness of strangers had inspired me to trust people again." "The kindness of strangers, in many small ways, and for various reasons, made me think that people are not all bad."

had done much to = had given great cause to = had resulted in = etc etc