Burning lips - i. e., “Lips glowing with, affection, uttering warm words of love,” joined with a malignant heart, are like a piece of broke…

Burning lips— that is, burning with love, while there is an evil heart within.

A potsherd covered with silver dross.…

Burning lips, and a wicked heart
Either burning with wrath and malice; breathing out threatenings and slaughter; pur…

A wicked heart disguising itself is like a potsherd covered with the dross of silver.