I have this Magic: The Gathering card flavor text: “To think some believe it peaceful to die in one's sleep.”
What exactly that “to think” means?
In this context, “to think” is like “I can't believe...” or “It is strange...”. The phrase on the card means “I can't believe that some people think it is peaceful to die in his/her sleep”. Examples:
It is kind of an antiquated phrase and isn't used all that often.
"to think" here refers to the meaning of both just think about it or rather take thought and can you imagine. I would suggest to separate it from the rest of the sentence by a comma.