In plain words
There are two main messages in the Rāmāyaṇa: one is Rāma's, the other is Rāvaṇa's. Satya is man's very form; Dharma is his very nature. Satya and Dharma are man's eyes. These themselves are the form of all the śāstras. So Rāma proclaimed to the world that man must practise Satya and Dharma, teach them, and so make his life fruitful. But Rāvaṇa was opposed to both Satya and Dharma. He would not accept Satya, and he would not practise Dharma. That is why he was utterly ruined. At the very end he gave the people a great message. “O people! Giving in to lust, I lost the sons I had fathered. Unable to curb my desires, I destroyed my own line. Unable to curb my attachment, I burnt my kingdom to ashes. In the end I burnt my own self to ashes. What did I gain? Only ill fame. So do not live as I did, against Satya and Dharma. Follow Satya and Dharma as Rāma did, and win good fame,” he said.
Good and bad do go together
Rāma is the one who won good fame; Rāvaṇa is the one who won ill fame. Fame and ill fame set out together, as a pair. There cannot be a Rāvaṇa without Rāma, or a Rāma without Rāvaṇa. The Rāmāyaṇa is the coming together of Rāma and Rāvaṇa. Bad is forever following close behind good. Just as behind a fair face like the disc of the moon there are dark curls coiled like rings, so behind the shining Dharma there is always the darkness called adharma. So good and bad, the two of them, do go together. They cannot be separated. The bond between good and bad is the same as the bond between our face and our hair. Had there been no Rāvaṇa at all, Rāma's fame could not have spread through the world. You must recognise such inner meanings in the Rāmāyaṇa.