What is the theme in The Silmarillion by J.R.R. Tolkien?

Betrayal recurs throughout this novel on both sides of the moral dichotomy; however, ironically, it seems to occur more frequently on the side designated as good. To begin with, Melkor betrays the other Ainur by his refusal to sing of Iluvatar's theme in harmony with the others. Then, he attempts to rule over the Valar on Ea. Iluvatar is aware of the fact that Men will betray the Valar and Elves, and their affinity with Melkor is given as the reason for their morality. After Melkor is released from his imprisonment of three ages, he betrays the Valar by pretending cooperation while secretly plotting retaliation.