The Tathāgata is also like this, for he is a father to the whole world. He has long ago completely gotten rid of all fear, distress, anxiety, ignorance, and blindness; has attained immeasurable insight, powers, and freedom from fear; and has gained great supernatural powers and wisdom. He has fully attained the perfections of skillful means and wisdom. His great mercy and compassion never stop. He always strives for benevolence and the enrichment of sentient beings. He was born into this threefold world, an old decaying burning house, in order to save sentient beings from the fires of birth, old age, disease, death, anxiety, sorrow, suffering, agony, folly, blindness, and the three poisons, and to teach and transform them, enabling them to reach supreme and perfect enlightenment.
The Lotus Sutra
Translation of the scriptural passage is based upon Gene Reeves, The Lotus Sutra: A Contemporary Translation of a Buddhist Classics, (Boston: Wisdom Publications, 2008), 115.
In short, the desire-realm is plagued by all three poisons, the form-realm by two poisons, and the formless-realm by one poison. In other words, the three realms are nothing but greed, aversion, and delusion. Seeing that all sentient beings are suffering from the fires of the three poisons, the Tathāgata has made the great sacrifice to be born in the human world in order to teach them how to stay away from the miseries and extinguish the fires of the three poisons. After he was born in the human world, he began to teach sentient beings the way to attain the fruition of the unsurpassed, complete and perfect enlightenment.
A Discourse on the Lotus Sutra, vol. 4, p. 295