The language of the poem is striking in its simplicity and there is very little figurative language used.
This simplicity creates a poignant tone as the poet observes the moving scene in front of him in precise detail.
We realise Heaney’s father was a man of few words. This knowledge makes his last words to his wife - the only direct speech in the sonnet - even more meaningful.
This is perhaps why the speaker says “we were overjoyed”.
There is a poignant irony in that when the father does share this very emotional memory after a lifetime of saying little, “She could not hear”.
The two specific words that his father called his mother – “good and girl” - have associations of youth. This reminds us - and perhaps the speaker too - that his mother and father were once young people.
The sense that the mother’s soul - or the mother as more than a memory – “penetrated” them is conveyed in the final phrase, “a pure change happened”.
It is almost as if what is no longer in the room - their mother - has “been emptied/ Into us to keep” and that she will make an impression on them all forever, despite having died.
In these last lines there is perhaps the idea that the poem is a celebration of the impact his mother had on him, as well as being a lament about her death.