For the sin... — As the text stands, it runs: Sin of their mouth, word of their lips, and they are taken in their pride, and cursing and lying they say; where some would supply a copula, “The sin of their mouth is the word of their lips,” which seems tautological nonsense. But, perhaps, we should take the accusative as adverb of instrument: By the sin of their mouth, by the word of their lips, let them even be taken in their pride.
And for cursing and lying which they speak. — That is, let their own malignant slanders, their blasphemous lies, recoil on their own heads; a frequent thought in the Psalms.