Duncan, through the first act of the play, shows why he is such a great King by using language that compliments and encourages all of his subjects and fighters. He welcomes Banquo and Macbeth equally, and shows that Macbeth is a fighter with whom he has been putting in the effort to watch and help him grow (comparing him to a tree). Malcolm echoes this language by promoting all of the Thanes to Earls, showing that he is investing his time and support into each of them like Duncan did.