What is the importance of diction in Do Not Go Gentle Into That Good Night?

Thomas structures the poem to offer a juxtaposition of light/dark, happy/sad, all which offer insight into the poet's mindset at the time. He uses diction to indicate that those who face death (as everyone does) should not face it without fighting for life. The form that Thomas uses is a villanelle, which is primarily used for poems depicting pastoral content. That he chooses this form offers, through diction, a type of irony as this is not pastoral in nature. Each stanza serves a purpose in the poem. The first stanza is a command, 2-5 are persuasive, while the 6th is directed toward his father encouraging him to fight.