The poem is arranged with a stream-of-consciousness approach, so summarizing it from beginning to end and sequentially is tricky.
Overall, the poem is about the growth in maturity the speaker has experienced to appreciate her mother's beauty and her struggles. As a child, she recalls that her mother sat in the dark, a lonely image, yet one the speaker knew she could depend on. She believed her mother both beautiful and powerful, alluding to the strengths of Samson in the Bible, which are reflected in her mother's hair, which is "three-quarters her height" on those dark evenings.
The speaker knows that her mother struggled. Some nights, she sat in the dark waiting for the speaker's father to return home, her mother stuck in an in-between twilight herself. The scene is lonely and somewhat tense; the fact that she would need to wait on her husband's arrival connotes a feeling of conflict. Her mother also had unclaimed dreams, and the speaker feels that perhaps her mother sat up at night hoping for a better life.
In her adulthood, the speaker finds an ease in the relationship with her mother. When she visits, she "pull[s]" a warm / comforting silence around / us...." They are both together and comfortable in silence. It seems that the mood of her mother's home has shifted in later years to reflect a scene of greater peace.
Through it all, the mother's lessons have remained important to the speaker. Her mother's beauty, dreams, and struggles become part of the legacy that the speaker will pass on to her son as they "bear the pleasures" as much as the "pains" of all that it means to be a family.