What were Hernando Cortes hidden motives in his letter to Emperor Charles V detailing his conquest of Montezuma's empire

Cortes' motives were to explain why he attacked the Aztecs even though he shouldn't have. He explained how they were immensely rich and had gold, as well as that they were pagans and would not accept Christianity, which is why he wanted to get a blessing from the King to ravage them and take everything.