Ross is the "messenger Thane," and if he visits you early in the play, all is good; but if visits you in the later acts, you had better sit down, because it's not good news.
In Act I, Ross brings good news. He tells Duncan of Macbeth and Banquo's valiance in defeat of Norway. Later, he tells Macbeth that he is Thane of Cawdor.
In Act IV, Ross informs Lady Macduff that her husband has left them for England. She calls her husband a coward, and right after Ross leaves, Lady Macduff and her son are murdered.
Later in Act IV, Ross goes to England to conference with Malcolm and Macduff, who plan invasion. Macduff asks on news of his family, but Ross is reluctant to relay it. Then, after some prodding, Ross says that Macduff's castle is surprised, his wife and child savagely murdered.
It's hard to tell whose side Ross is on. He is like a character in the audience--he knows what we know. His sadistic messages are little reminders to us as well.
It should also be noted in this regard that Rosse’s arrival is an extremely significant point in this Shakespearean tragedy. First of all, it is Rosse who first delivers the news of Macduff’s loss to Macduff. Secondly, his arrival turns the play into a new direction. Before his arrival Macduff has been continuously trying to persuade Malcolm to confront Macbeth. Rosse’s news turns out as an invigorating power which directly cheers Malcolm to destroy Macbeth: “Be comforted : / Let’s make us med’cines of our great revenge, / To cure this deadly grief.” (lines 213-215).
Ross tells Malcolm and Macduff that Scotland is in chaos. He describes the situation in harrowing detail, saying that "sighs and groans and shrieks...rend the air...violent sorrow seems a modern ecstasy...good men's lives expire before the flowers in their caps" (IV, iii, 169-173). Ross urges Malcolm, whose "eye in Scotland would create soldiers, make our women fight, to doff their dire distresses" (IV, iii, 187-189) to come quickly to the motherland's aid and fight the tyrant Macbeth.
Ross is reluctant to relate the worst of the news, however, until he is pressed by Macduff. He tells Macduff, "your castle is surpirsed, your wife and babes savagely slaughtered" (IV, iii, 205-206). Macduff's entire family has been wiped out in a most heinous manner, and Macduff, devastated, vows to have his revenge against Macbeth.
Ross arrives and tells Malcolm and Macduff that Macduff's wife, children, servants and everyone in his castle were killed.
Ross, a Scottish nobleman first appears in Macbeth in Act 1 Scene 11. He arrives shortly after the bleeding captain delivers his account of the battlefield to King Duncan. Ross endorses the captain's report with his account of Macbeth and Banquo's victory over the traitorous Thane of Cawdor and the King of Norway. He tells how the Norwegian was forced to beg for a truce and had to pay ten thoudand dollars for his surrender.
Later on in Scene 111 Ross delivers to Macbeth the news of the King's joy on hearing of his valour and instructed that the title Thane of Cawdor be bestowed upon him . Macbeth is a bit shaken at this since the Thane of Cawdor has not been officially declared dead. It also endorses the witches forecast so far.