Sc. 3, lines 65–67: what metaphor does macduff make in these lines? why is this metaphor effective?

In "The Tragedy of Macbeth", by William Shakespeare, Scene III, Lines 65-67 the metaphor that MacDuff makes in these lines is "Approach the chamber, and destroy/your sight/With a new Gorgon." Gorgon, in Greek mythology, are three sisters that have snakes for hair and have the power to turn he who looks at them into stones. The sight of King Duncan being dead will turn them into stone. From then on everything becomes unnatural in the play.

c. to depict the cunningness of the federal soldiers