There are a few important clues about the poet's attitude that appear both in the poem and from the very start in the title. The title itself suggests a look backwards, foreshadowing the particular lines in the poem itself that demonstrate how the speaker's attitude has changed since the time depicted in the poem.
The main indications come in the final stanza of the poem. The juxtaposition of the image of the younger man "speaking indifferently to" his father and the image of the father, tired from his labors making sure to perform one more, that of "driv[ing] out the cold" makes it clear that the younger man is no longer indifferent to this particular labor of love. He did not notice it then, did not thank him, but he remembers it now.
Of course the last line with its rhetorical question is the most poignant:
What did I know, what did I know of love’s austere and lonely offices?The question suggests the speaker now questions the lack of understanding and knowledge he had at the time. The speaker is clearly now filled with regret at the lack of knowledge he had at the time.