Most people who regret something wish they could undo the deed. Donne's speaker wishes for something odder: that he could take his tears back. "O might those sighs and tears return again / Into my breast and eyes, which I have spent." Sorrow here is treated like money that has been squandered and might somehow be refunded. His reason is almost practical. He wants to weep again "with some fruit," in "holy discontent," because the mourning he has already done was "in vain."
What went wrong with those earlier tears? The poem points to "Idolatry" but never names the idol. Judging by the language, the speaker gave to something earthly the passion that belonged to God, though that is an inference, since the text says only that his eyes "did waste" showers of rain. The image works twice over. Rain ought to feed a crop, and the earlier word "fruit" sets up the farming picture, so his tears fell on barren ground and grew nothing. Even his grief was badly spent.
Then comes the knot at the centre of the poem: "That sufferance was my sin; now I repent; / 'Cause I did suffer I must suffer pain." The word "suffer" turns up three times, and its meaning slides each time. First the suffering is itself the offence, then it becomes the penalty. Line 8 sounds like a legal verdict, a neat "because… therefore" in which the speaker convicts himself in the very syntax. The octave rhymes abba abba, a tight Petrarchan pattern with only two rhyme sounds, and that repetition adds to the feeling of being boxed in. The exclamations of lines 5 and 6, "what showers of rain / Mine eyes did waste! what griefs my heart did rent!", break up the steady iambic pentameter and make him sound breathless, as if the memory is still hurting.
At line 9 the poem turns, and the voice changes with it. Donne offers a quick gallery of other sinners: the "hydropic drunkard," the "night-scouting thief," the "itchy lecher," the "self-tickling proud." Hydropic refers to dropsy, an illness that swells the body with fluid while leaving the sufferer raging with thirst. That is a cruel irony in a poem full of water and wasted tears. The labels are physical, even faintly comic: itching, tickling, scouting in the dark. Donne makes sin look like an appetite of the body, pride included. Each of these figures has one comfort the speaker lacks. They can remember "past joys" as "relief / Of comming ills," so their pleasure at least gives them something to hold on to when punishment looms.
The speaker has no such store. "To (poor) me is allowed / No ease." The brackets around "poor" are intriguing. They could be self-pity, or a dry, bitter aside. Either way, the word seems to slip out of him almost against his will. His past offered no joys to recall, because his sin was grief, and grief is exactly what he is stuck with now.
The final line seals the trap with a chiasmus, a mirrored pattern: grief "hath been / Th' effect and cause, the punishment and sin." Cause and effect, sin and punishment, swap places until they cannot be told apart. The couplet rhymes "been" with "sin" (it works if you say "been" short), so the sound itself ties his existence to his guilt. Nothing in the ending offers consolation, and the sonnet closes on a loop.
That is a large part of what makes the poem worth reading. Devotional poetry might be expected to move towards comfort, yet Donne lets the argument run and refuses to rescue the speaker. He makes theological anxiety feel like a logical puzzle with no exit, and he gives it a body through the drunkard, the lecher and the thief. The result is a very honest portrait of a mind that cannot stop analysing its own guilt, and that is why it still feels modern.