Great literature is replete with metaphors and similes which, by making unsual comparisons between ideas and things, enable readers understandings of life.

In Scene 2 of Act IV, when the murderers enter, they are insulted by Macduff's son, and one stabs the boys saying, "Young fry of treachery," a metaphor for the boy's being the son of a man who is a traitor.  In the following scene, Macduff's first words contain two similes [comparisons of unlike things using the words as or like]:

Let us rather

Hold fast the mortal sword, and like good men

Bestride our down-fall'n birthdom.

Each new morn New widows howl, new orphans cry, new sorrows

Strike heaven on the face, that it resounds

As if it felt with Scotland and yelled out

Like a syllable of dolor. (IV,iii,3-9)

Then, in line 22 of this scene, Malcolm says,

Though all things foul would wear the brows of grace,

Yet grace must still look so. (IV,iii,22)

This line means that his thoughts cannot change what a person is; things may look good, but be filthy; nevertheless, good must still resemble them when they are disguised.  "The brows of grace" is the appearance of seeming good.

Later in the scene, Malcolm uses a simile as he says,

black Macbeth

Will seem as pure as snow, and the poor state

Esteem him as a lamb, being compared

With my confineless harms. (IV,iii, 59-61)

Further in this scene, Malcom employs a metaphor as he says, "Pour the sweet milk of concord into hell" as he states that he would cause discord in the world, destroying peace.

When I look at Act IV, Scene 2, I come across a metaphor quite early on.

In this scene, Lady Macduff is talking to Ross.  Macduff, her husband, has run off to England.  He has gone down there so he can help get a rebellion going against Macbeth.  But Lady Macduff does not know that and she is really mad that he has gone.  She thinks he should have stayed to protect his family.

Ross basically tells her to calm down and then uses the metaphor that they are a ship tossed about on a wild ocean.  He says

But cruel are the times, when we are traitors
And do not know ourselves, when we hold rumour
From what we fear, yet know not what we fear,
But float upon a wild and violent sea
Each way and move.