In John Donne's Holy Sonnet X, Death be not proud, death is apostrophized, or directly addressed as though it were a person rather than an abstraction. The speaker remonstrates with death not to display pride, as humans do when others hail them as "Mighty and dreadful." In lines 1 and 2, the speaker insists death is neither all-powerful nor worthy of awe and fear.
The people death appears to have conquered and deprived of further existence are not dead, nor can death ever claim the life of the speaker. Though the personification of death in line 1 seems to be dignified by a proper noun, we now see that the capitalized name was the opening line of the sentence. Thereafter, the lower-case "d" demeans the personage to a generic concept rather than an individual or a proper noun.
The speaker must now prove that those whom death thinks it has overthrown have not died. The argument of the second quatrain is that "rest and sleep" are death's counterfeits. It is true that we derive pleasure from rest and sleep. If "pictures" or resemblances of death are as refreshing and relaxing to body and spirit as they are, then (the speaker's spurious logic argues) the real thing must be even more salubrious. The best of men are ready and willing to seek the ultimate resting place.
Derisively, the speaker calls death a "slave," forced to do the bidding of "fate, chance, kings, and desperate men," and to live in the slaves' quarters with unwholesome roommates like "poison, war, and sickness." Furthermore, drugs distilled of poppies and magicians' charms or spells are capable of inducing sleep that is as good or better than that of death.. Therefore, why should the base person death swell with pride at his might and power?
What is claimed in the concluding couplet is that after the short nap imposed upon us by death, we awake to the eternal life of salvation. And in that life of the soul, death shall have no dominion (to borrow a line from Dylan Thomas). Death will die.
The sonnet is a mixture of the Italian and English sonnet forms, a rarity in the early 17th century when poets felt a greater necessity to adhere to the prescribed forms than do modern sonneteers. The octave has the conventional Italian rhyme scheme abbaabba. However the sestet is not what one would expect. The English (or Shakespearean) sonnet ordinarily begins with three quatrains each with its own alternating rhyme abab cdcd efef and concludes with a rhymed couplet gg.. The sestet of the Italian sonnet has its own unity and may rhyme cdecde or cdcdcd. This poem has a conventional Italian octave, then a third quatrain with the Italianate cddc rhyme scheme and an English closing couplet.
Generally, the English sonnet progresses to a surprising turn (or volta) in the concluding couplet. The Italian sonnet makes its dramatic turn between opening octave and concluding sestet. Since lines 13 and 14 are not a rhymed couplet (often indented in the English form), they are less emphatic, less like a punch line. So we need to ask why in this poem Donne finds it most suitable to commingle the sonnet forms.
The logical foundation of the argument is easily assailable. The speaker knows this but covers the shaky logic with bravado and insulting treatment of death. Although the sleeping and the dead resemble each other superficially, there is a huge difference between breathing and not breathing, having a pulse and having no pulse. The immortality of the soul and eternal life beyond the grave cannot be proven but must be accepted as an article of faith.
Poison, war and sickness are horrible facts of life, and only a poet can relegate them to the lowly status of cellmates of the slave death. The ultimate illogicality is "Death, thou shalt die!" Death was never really a living organism and thus cannot die. It is a paradox as contrary to logic as a three-personed God that is a Unity. No one has returned from the realm of immortality and salvation to give empirical proof that it exists. The absence of provable certitude requires that the vacuum be filled by faith. This was stated in quatrain one, and the words of the concluding couplet, rhyming with lines 1 and 4, establish a circle, a geometrical figure we recognize and accept despite the illogicality of it having no beginning and no end.