A letter is communication. Communication of information and communication of feelings. Letters from my bank have little feelings (and sometimes little information too). Letters from individual people have a lot of feelings, even if they didn't intend there to be. It takes a lot of effort to write a letter. You have to think of what to say all in one go, you have to get out paper and probably handwrite it, you have to go to the post office, you have to pay for stamps, you have to wait for deli...
