What is one dominant theme in Those Winter Sundays by Robert Hayden and how does the diction, speaker, and tone help in developing that them?

The dominant theme in "Those Winter Sundays" is the speaker's love for his father, mixed with a guilt for perhaps not expressing that love more fully. He, the speaker, reminisces about the sacrifices his father made for him when he was younger. The father worked hard, polished his son's shoes, and woke early to start the fires so that the house was warm when it was time for the son to rise. The father did all of this but the son, perhaps unaware or unthinking, spoke to the father "indifferently." This poem was perhaps written to redress that indifference.
The love of the speaker towards the father is implied throughout the poem by the simple account of the sacrifices that the father made for the son. For example, phrases such as "my father got up early" and "cracked hands that ached / from labor." The speaker's guilt is implied by the simple sentence, "No one thanked him." and also the rhetorical question that concludes the poem:

"What did I know, what did I know / of love's austere and lonely offices?"

This rhetorical question, as well as the repetition at the beginning of it, creates a tone of self-critical guilt and regret. We can all empathize with the speaker if we have had such a father, as we, like the speaker, probably take for granted many of the sacrifices that our fathers make for us.