"As imperceptibly as grief" - this simile introduces the theme of loss or absence as well as suggesting that like summer passing grief takes a long time to fade away.
"As imperceptibly" - The word "imperceptibly" suggests something happening slowly over time without being noticed.
What is the effect of the capitalisation of the nouns: Grief, Summer, Perfidy?
Emphasis on how important they are, it almost personifies them.
There is also a religious link with them being capitalised, indicating that Dickinson's grief has her thinking in a deeper more spritual way.
Throughout the poem, everyday language suggests that grief is a normal thing to experience.
"A Quietness distilled"-suggests that grief is intense and long-lasting
"Twilight"- Time imagery could suggest the passing of time therefore the cycle of life and death and therefore grief is inevitable.
Twilight is also a time of change, from day to night, or night into day- it could suggest hope as better things are soon to come. Or it could be discouraging as one enters even more darkness.
"Or nature spending time with herself" What is the significance of nature being personified?
Personified as not just a woman but as a woman who is ISOLATED which could reflected in Dickinson as she often hid away from society in her home.
What do the words "Quietness" and "Sequestered" suggest about grief?
The noun "Quietness" and the adjective "Sequestered" create the impression associated with gird is peaceful and comforting