Toward the end of the movie Thor, the hero, banished to earth and stripped of his powers, finally puts his arrogance aside. He is willing to die, rather than conquer, because his friends are in danger. It is this willingness that makes him worthy again to take up Mjolnir and wield the power of Thor.
Whether Thor's character development leads believably to his moment of sacrifice may be debated.
I don't believe, however, that the worth of his sacrifice may be. After all, "no one has greater love than this, to lay down one’s life for one’s friends." (John 15:13) By laying down his life to protect his friends, human and Asgardian, he proves himself worthy of the power of Thor.
Reminiscent of other Biblical scenes, Thor receives the blessing of his father from above. The power descends on him - a blazing hammer, rather than a tongue of fire or a dove, in this case (Mt 3:16) - and he is bathed in light and changed before their eyes. (Mt 17:2)