Final answer:
Ross brings Macbeth news of the king's pleasure in his battle success and that he has been named the new Thane of Cawdor, which aligns with the witches' prophecy.
Step-by-step explanation:
The news that Ross brings to Macbeth in Act I of Shakespeare's play is twofold. Firstly, he informs Macbeth that the king has heard of his valiant success in battle and is pleased with his actions. Following this, Ross delivers the message that King Duncan has decreed Macbeth the new Thane of Cawdor, as the previous thane is to be executed for treason.
Lady Macbeth refers to this news as great because it corresponds to the prophecy given by the witches earlier in the play, which stated that Macbeth would become Thane of Cawdor and eventually the king.