Psalms 5:9
For there is no faithfulness in their mouth; their inward part is very wickedness; their throat is an open sepulchre; they flatter with their tongue. For there is no faithfulness in their mouth; their inward part is very wickedness; their throat is an open sepulchre; they flatter with their tongue.
Psalm 5:9 sets forth the unrighteous side of speech, as one of the two distinguishing features of speech, righteousness and unrighteousness. It describes the workers of iniquity, the bloody and deceitful, the enemies who have rebelled against God. Their mouths contain no faithfulness, and their flattering tongues cannot be trusted because their inward part is very wickedness, deeply wicked within.
Their throat is likened to an open sepulchre, an open grave. The verse belongs to a prayer asking God to lead the speaker in righteousness, to lead rightly, in the face of such enemies. Such speech reveals the talent of speech as a mighty power for evil, which must be carefully guarded. For this corrupt speech its users will be destroyed, will fall by their own counsels, and will be cast out in the multitude of their transgressions, in contrast to the righteous who come into God's house, worship toward His holy temple, are led in His righteousness, put their trust in Him, rejoice and shout for joy, and are defended, blessed, and compassed with favor as with a shield.