Charles H. Spurgeon on Psalms 52:2

Thy tongue deviseth mischiefs. Thou speakest with an ulterior design. The information given was for Saul's assistance apparently, but in very deed in his heart the Edomite hated the priests of the God of Jacob. It is a mark of deep depravity, when the evil spoken is craftily intended to promote a yet greater evil. Like a sharp razor, working deceitfully. David represents the false tongue as being effectual for mischief, like a razor which, unawares to the person operated on, is making him bald; so softly and deftly do Oriental barbers perform their work. Or he may mean that as with a razor a man's throat may be cut very speedily, under the pretence of shaving him, even thus keenly, basely, but effectually Doeg destroyed the band of the priests. Whetted by malice, and guided by craft, he did his cruel work with accursed thoroughness.