Though the mills of God grind slowly, yet they grind exceeding small; Though with patience he stands waiting, with exactness grinds he all.
Why it works
At just two lines, the entire poem operates as a single epigram: the first line sets up a paradox (slowness vs. thoroughness), and the second delivers the sharp, closing insight — that divine justice misses nothing — clinched by the inverted syntax of "grinds he all," which gives the final word a punchy, epigrammatic finality.