The suggestion is that the title was like the Prince of Wales: it was the title of the heir apparent.
Malcolm being named Prince of Cumberland makes him the heir apparent to the Scottish throne, putting him in a strong position to challenge Macbeth for the crown. It also highlights the legitimate claim Malcolm has to the throne, further emphasizing Macbeth's position as a usurper.
In Act 1, Scene 4 of "Macbeth," Banquo is honored by being named a nobleman and receiving the title of the Thane of Lochaber. Malcolm, the Prince of Cumberland, is also honored by being declared heir to the Scottish throne by King Duncan.
I suppose you are asking about Malcolm being made Prince of Cumberland. The idea was that he was being marked out as the heir apparent--sort of like making someone Prince of Wales.
Macbeth has "black and deep desires" regarding dutchman's son and heir, malcolm.
After the successful battle at the beginning of Act I, Duncan rewards Macbeth for being a war hero by giving him the title Thane of Cawdor. In the same scene (Act I Scene 4) he rewards Malcolm for no particular reason with the title Prince of Cumberland, and then says, "From hence to Inverness, and bind us further to you." Inverness is the city where Macbeth lives, and Duncan is in effect saying, "Hey guys, the party's at the Macbeths'!" This is significant because it will put him in range of Lady Macbeth, who will be the death of him.
The contents of Macbeth's letter to Lady Macbeth was about Macbeth's prediction from the 3 witches he met in the beginning - about him being the Thane of Cawdor (thane means prince/king) and then the King of Scotland. Lady Macbeth becomes hyped, because she was waiting for the chance to have all the power to be a queen.
Malcolm was a suspect in the murder of King Duncan because he fled Scotland immediately after his father's death, which made him look guilty of being involved in the assassination plot. Macbeth, the true culprit, used Malcolm's hasty departure to cast suspicion on him and secure his path to the throne.
yes
Macbeth killed King Duncan after hearing the witches' prophecies and being urged on by his wife, Lady Macbeth
she talked him into killing the King by accusing Macbeth of being weak and cowardly
The entrance of Macbeth [c. 1014-August 15, 1057] in Act 1 Scene 4 of the Shakespearean play was dramatically ironic. In Scene 3, he had received the witches' predictions of noble and royal career moves in his future. He also had received the news of his receipt of the powerful title and profitable properties of the disgraced Thane of Cawdor. So in Scene 4 Macbeth brought royal expectations to a meeting of King Duncan I [d. August 14, 1040] and the leading noblemen of Scotland. Ironically, those expectations quickly were dashed. Shortly after his arrival, he found out that Malcolm[d. November 13, 1093] was being given the title of Prince of Cumberland by King Duncan I [d. August 14, 1040] of Scotland. By law, the principality of Cumberland stood between Macbeth's royal ambitions, which recently had been encouraged by the witches' predictions, and the legal realities of succession to the throne of Scotland.
After killing Duncan, Macbeth could not sleep. He feels the guilt and is terrified