What effect does the repetition of "Do not go gentle into that good night" and Rage, rage against the dying light" have?

In his emotional and moving plea to his father to embrace
life until the very end, the repetition of the lines cited above increase the intensity
and personal meaning of Dylan Thomas's poem.

Despite the
inevitability of death, Thomas as the speaker of this poem feels that by "raging against
the light," or affirming life, his father can die with dignity as opposed to "going
gently," or weakly.  Thomas's arrangement of his poem into a villanelle form also
underscores the the intensity rhetorical argument of his work.  Thus, the repetition of
lines as a rhetorical form adds emphasis and meaning to the argument.  And, because the
villanelle's form resists narrative development, this form strengthens the speaker's
insistence upon his father's affirmation of life.