The relationship between David and his father is rocky to say the least. David’s father is oppressive and tyrannically religious. Uncle Axel, on the other hand, is kind to David and provides him with advice.
David comments that he is lucky that it is Uncle Axel and not someone else who discovers that David and Rosalind are telepaths. Being a telepath means you are a mutant, which means they will expel you or kill you. David describes him as his “best friend among the grown-ups” (ch 4). When Axel realizes that David has special powers, he makes him promise not tell anyone and not to talk to Rosalind out loud.
'It also helps to make things a lot more dangerous, for both of you. I want you to make another promise -- that you'll never do it out loud any more.' (ch 4)
While Axel is helpful and supportive of David, his father is the opposite. His father is a cruel, intractable man. He is so concerned with David’s religious upbringing that he treats him harshly and even cruelly.
My father's faith was bred into his bones, his principles were his sinews, and both responded to a mind richly stored with examples from the Bible, and from Nicholson's Repentances. (ch 2)
David is afraid of his father, and seems to have no affection for him. With his father, all is black and white. There are no innocent mistakes. For example, when David accidentally says he could have used another hand, his father beats him for it because it would make him a mutant.