When discussing the main ideas or points in poetry, one tends to name the themes defined in the poem as the main points.
In regards to Robert Hayden's "Those Winter Sunday," one theme (or main point) revolves around both the speakers lack of knowledge as a child and his present knowledge as an adult (regarding the invisible sacrifices made by his father). The child speaker failed to recognize what his father did, for him and his family. As an adult, the speaker can look back and recognize the sacrifices made by the father.
Another theme, or main point, raised is pain. The pain the father felt (because of his "cracked hands that ached from labor") and the emotional pain the speaker feels because he cannot thank his father for his sacrifices both illuminate the main point of the importance of pain.
Lastly, the poem draws attention to the complexities and challenges within a family dynamic. The father would call out to the son, and the son would "speak indifferently" to him. Even though his father had insured the room was warm and the speaker's shoes were polished, the speaker did not care. This, later in life, the speaker finds challenging.