Through his lines Duncan shows that he is a kind and thoughtful king. In the scene 4 lines he shows that he believes in Macbeth and will continue to help him grow. He uses the imagery of a tree that he has planted and now will nurture ("I have begun to plant thee, and will labour / To make thee full of growing"). He also makes sure to praise Banquo which shows that he is not only focused on Macbeth but he respects all of his people.
The lines in scene 6 show again how kind and warm Duncan is. He thanks and gives praise to Lady Macbeth for welcoming everyone into her home. This shows that he is as kind and gracious to the women as he is to the men.
Showing how kind and caring Duncan is in these scenes makes it much more difficult for Macbeth to feel okay about killing him. He knows that he is gentle and loves Duncan, which is emphasized by these quotes.
