How does the point of view in Robert Hayden's poem "Those Winter Sundays" help shape the story and our interpretation of it and what thematic life lesson or moral does it convey?

This poem is written from a first person objective point of view.  This means that the speaker is a participant in the action and that he uses the first person pronoun "I."  The "objective" part refers to the fact that the speaker is reflecting back on events and retelling them while using the past tense (as though he were, from this vantage point in time, more capable of objectivity than if he were telling the events while they occurred).  In other words, the speaker is now an adult, but he was just a boy when the events of the poem took place.
Since the speaker is now a grown man, he has more emotional maturity than he did as a child.  The final lines, "What did I know, what did I know / of love's austere and lonely offices?" help us to understand that the narrator recognizes now what he could not then: how much his father loved him.  It sounds like his dad was not really the warm and fuzzy type—he was tough, and perhaps even spoke harshly to his family (a conclusion we might draw from the narrator's reference to "fearing the chronic angers of that house").  
As a child, the narrator did not realize that getting up early on his one day off to light fires and warm the house was his father's way of showing love.  Nor did he realize the same emotion prompted his dad to polish his shoes for him.  Because he failed to see this as loving, he spoke "indifferently to him" and never "thanked him."
Had the speaker narrated the poem as a child, it would have been a dramatically different poem: the boy did not understand his father's love and likely had strong, negative feelings about the man.  It might have been an angry poem.  Instead, the grown man thinks back and realizes that his boyhood perception was wrong, perhaps something he has realized as a result of having his own children and seeing, firsthand, how much a parent does that goes unappreciated at the time.
This poem conveys the somewhat tragic idea that children do not fully appreciate their parents' love until they have grown up themselves. It also leads us to the theme that love is not all hearts and kisses; it often involves unappreciated sacrifice for those we care about.