1 Macduff and Malcolm argued
Malcolm was eager to fight Macbeth as they both continuously argued about the right thing to do.
2 Malcolm did not trust himself
Malcolm was full of greed and lust. He knew that a part of him was evil. Furthermore, he did not even want to let people know about how bad he is.
3 Macduff reassured Malcolm
On the contrary, Macduff started to bolster Malcolm's confidence to rule. He tried to convince him that Malcolm is a good ruler if he takes over.
4 Malcolm trusted Macduff
Malcolm started gaining trust and believed that Macduff was a genuine person. Malcolm then told Macduff that he was lying about himself that he is bad in order to check Macduff's response in that situation. However, Malcolm started trusting him once he found the reaction of Macduff.
5 Malcolm will fight Macbeth
Malcolm told Macduff that the army is getting prepared for fighting against Macbeth. (See Summary of Macbeth Act 5)
6 King Edward heals people
King Edward has a unique power that can heal anyone. Malcolm knew about this and told this to Macduff about King Edward's magical power that was blessed with.
7 Ross arrived with news
Ross informed Macduff that some people are planning to fight against Macbeth. Ross asked those people to come back to Scotland and instigate people, and convince them to fight against Macbeth. (See Summary of Macbeth Act 4)
8 Macduff’s family was killed
Ross gave Macduff a piece of information that everyone in his family, including his wife, children, and servants, were killed.
9 Macduff wanted revenge
Macduff wanted to retaliate for wrong. All his sorrow got converted into intense aggression.