For there is no faithfulness in their mouth; or, no steadfastness—"no sincerity" (Kay, Cheyne); see the comment on Psalms 5:6. Their inward part is very wickedness; literally, wickednesses; i.e. nothing but wickedness.
Their throat is an open sepulchre. "Emitting the noisome exhalations of a putrid heart" (Bishop Horns). They flatter with their tongue; literally, they make smooth their tongues, which may, perhaps, include flattery, but points rather to smooth arguments, specious reasonings, and the habit of making the worse appear the better cause.
The last two clauses of this verse are quoted by St. Paul (Romans 3:13), and applied generally to the character of the ungodly.