Ross first relayed the message to Lady Macduff regarding her husband. He said that Macduff has left in order to go to England. Lady Macduff did not like this message because, in her opinion, her husband is a coward for doing this. Ross leaves at night and soon after that, Lady Macduff and her son are murdered.
Later in the same act, Ross had to tell Macduff the truth about his family. He did not want to say it in the beginning because Macduff was planning his next move but when he was told about the murder of his wife and child, he was surprised and he felt a lot of emotions after.
Ross tells Macduff that his family has been killed. Macduff is grieving and he vows to get revenge on Macbeth. Malcolm tells Macduff to turn his grief to anger and they plan their invasion of Scotland to overthrow Macbeth.
The news that Ross brings to Macduff, is the fact that Macbeth had sent an army towards his castle, killing his wives and children. Upon learning about such an event, Macduff was overcome with sadness and sorrow, grief, anger, and was desperatelywanting revenge on Macbeth for his actions.