Malcolm, Siward, Ross, and others enter. Ross tells Siward of Young Siward's death. Siward asks if his son died from wounds on the front or back. Ross replies the front. Siward is content, denying Malcolm's comment that his son is worth more mourning than that.
Siward is an ambiguous part of an otherwise happy ending. Siward prizes strength and courage above all things, even love for his family. Might he one day become another Macbeth?
Macduff enters, carrying Macbeth's severed head. He proclaims Malcolm to be King of Scotland and swears his loyalty.
Macduff shows his loyalty to King and country.
Malcolm accepts the thanes' loyalty and makes them all earls (a higher rank). He pledges to "plant" a new peace, and to heal the wounds Macbeth and his "fiend-like queen" (5.11.35) inflicted on Scotland.
Malcolm returns Scotland to political order, as his use of nature metaphors shows. Malcolm wants to make his country great, not himself.