Motivations
Pathos
"Do you find your patience so predominant in your nature, that you can let this go?"
Nature out of order
"It was the owl that shrieked, the fatal bellman, which gives the stern'st good-night
Lady Macbeth saves Macbeth from talking too much
"Help me hence, ho!"
A Roman leader, or one of Shakespeare's own plays
"Under him my genius is rebuked, as it is said Mark Antony's was by Caesar"
Malcolm flees to England
"Thither Macduff is gone to pray the holy king, upon his aid To wake Northumberland and warlike Siward"
Falsehood, hiding true character
"There's daggers in men's smiles, the near in blood, the nearer bloody"
A murderer's delicate sensibilities
"O gentle lady, 'tis not for you to hear what I can speak: the repetition, in a woman's ear, would murder as it fell."
Roman god of the sea
"Will all Neptune's great ocean wash this blood clean from my hand?"
Logos
"Both of you know Banquo was your enemy"
Blood on one's hands
"This my hand will rather the multitudinous seas incarnadine, making the green one red"
Third murderer lets Fleance escape
One can only guess...