If he was my friend, I would give consolation to Kafka saying that it was important that he wrote that letter, because the healing is in the writing process. But even if his father read it, he wouldn't ask for forgiveness anyhow... I know from experience that the only way you can deal with a violent, condescending, horrifying parent is dark humour. You must give up all hope on "reaching" to that person. But isn't there also a wisdom and humility in accepting the " impossibility" of communicating with certain type of cruel and sick people?