Some parents had a bad experience from their childhood, and unfortunately postpone it on their own children.
And some (brave as peter) draw from them to extract the kindness and understanding and transform it into love.
The last words of the father of peter in the documentary are "when you understand that ...", he speaking to himself and he can not (by pride) turn into love, because he thinks it is too late or is it even a poor person.
I wish the father of peter to emulate his son, he will never find rest and peace without it.
I am not a believer (but I read most of the major works on monotheist), and i do not think the command "respect your father and your mother" be the most important.
For me the concept of forgiveness is the most important, and as Peter's father will not forgive his son, he can not forgive to himself.