The main significance of this scene is that it gives the audience a view of Macbeth's character up to this point in his life and shows the rewards that Duncan is going to give him for his service. At this point in is career, Macbeth has been seen as a noble supporter for his King, Duncan, fighting against a disloyal thane of Cawdor. For his service, Duncan is going to give Macbeth the office and lands of the Thane of Cawdor. It is a worthy prize for Macbeth's service and Duncan is doing right by Macbeth in giving it to him.
The scene is significant to the rest of the play because it highlights the severity of Macbeth's treason and shows how the temptation provided by the witches and his sin in falling to that temptation changes his character.
This scene is important because it shows Macbeth's characteristics before he listens to the witches' prophecies. It presents Macbeth as a brave and noble general who fights valiantly for his country, Scotland, and his king, Duncan. He seems to be loyal to the king and it seems due to Macbeth's actions in the battlefield, he is going to be rewarded by the title of Thane of Cawdor - since the original incumbent turns out to be a traitor.
With reference to the whole play of "Macbeth", this scene is very important because it shows what Macbeth's character is like before its deterioration started. Also, it highlights the atrociousness of Macbeth's murder of Duncan. It is also important to the plot of the play because it shows the normal order of society before the disorder starts, which, in tragedies, is solved through the death of a person. In this one scene we get the idea of the positions of most of the major characters in the society so that we can understand what starts to go wrong from the next scene.