Only tonight/ I am happy and sad.
This stanza begins with "Only tonight" which asserts that this transition, this journey is a singular experience. She expresses contradictory, uncertain emotions. Perhaps she is sad to be leaving her mother behind or even mourning the end of her childhood. But she is also positive about what the future holds for her and that fact she still has this connection with her past to take with her.
Like a child/ who stood at the end of summer
She compares her feelings to those of moving from childhood to adulthood to the change of seasons. It is the "end of summer" which links back to her switching the "too blue" sky for "cool grey".
The delight and innocence of childhood is ending. She alludes to the archetypal image of a child by the frog pond, but this time it is a "green, erotic pond". There is a slight contradiction here as "green" has connotations of naivety while "erotic" connotes a more adult theme. This juxtaposition could reflect the innocent child coming face to face with the wider world.
Perhaps because of this, she returns to her mother's phrases "The day and ever", repeating them like a comforting mantra. No matter what she has to confront, she has her mother's voice within her, giving her strength.
Thus the poem concludes with:
I am homesick, free, in love with the way my mother speaks
These lines unite some of the contradictions from earlier in the poem. She is "homesick" for her childhood, her past, her mother, but she also feels "free" to establish her new identity, to stride forward, to continue travelling "down England" and further.
The line break just after "in love" leaves it hanging for a moment, as if she is "in love" with life, a love which was given to her earlier by her mother. The final line then confirms this. It returns to the title and tells us that she is pleased to have such a bond with her past. She loves that in this "slow evening" her mother's voice comes back to her and will continue to do so for "ever."