"threescore years and ten,..."
See in text (Text of the Poem)
This phrase, “threescore years and ten,” comes from Psalms 90: “the days of our years are threescore years and ten; and if by reason of strength they be fourscore years, yet is their strength labor and sorrow; for it is soon cut off, and we fly away.” In this passage, people are stated to live to 70 years old; they can live to 80, but only with great labor and sorrow, perhaps because they know there is a limit to their strength and their death is inevitable. Shakespeare also references this particular measurement of time in Macbeth. The speaker uses this allusion to explain his confidence that he will live 70 years and appears to draw comfort from the knowledge of this fixed time.