The difference between Buddhas and demons is that Buddhas have no hatred, while demons do. The Buddha accomplished Buddhahood with the help of demons. When the Buddha was about to become enlightened beneath the Bodhi tree, the heavenly demons became furious. They dispatched demon armies to threaten the Buddha and demon women to seduce him. However, the Buddha remained unmoved and overcame the demons with his samadhi power. Thus, he realized Buddhahood. The Buddha doesn't hate demons. Demons become demons because they like to fight and quarrel. It is said,
Fighting involves thoughts of victory and defeat,
And is in opposition to the Way.
Giving rise to the thought of the Four Marks,
How can one obtain samadhi?
When demons are frustrated in their struggle to be number one, they become angry, jealous and obstructive. Whoever behaves that way is a demon and will never be able to attain Buddhahood.
The spiritual powers of demons and the spiritual powers of Buddhas are pretty much the same. The only difference is that while the Buddhas' spiritual powers are proper, those of demons are deviant. It is said that “the deviant cannot overcome the proper.” Since demons are ultimately inferior to Buddhas, they humbly bow to the ground, and take refuge in the Buddhas.
Buddhas feel pity and compassion toward living beings. They would never oppose demons. Instead, they influence demons with their virtue, until the demons are moved to submit wholeheartedly. One of the Eight Signs of Realizing the Way is that of “subduing demons.” However, it would be more fitting to say that Buddhas “influence and convert” demons, because Buddhas don't use force to subdue demons. If they subdued demons, they would have the view of self, the view of others, the view of living beings, and the view of a life span. Having these four views, they couldn't have become Buddhas.
How does a Buddha cause demons to surrender? A Buddha has the Four Boundless Thoughts of kindness, compassion, joy, and equanimity. No matter how the demons attack and harm the Buddha, he responds with kindness, compassion, joy, and equanimity and uses his virtuous conduct to influence them. Since Buddhas know the causes and effects of the past and future, when demons come to harm them, they know that it's due to feelings of enmity left over from former lives. Therefore, they don't mind it; they suffer demonic disturbances with perfect peace of mind.
How do demons become demons? Five kinds of poisonous energies—hatred, resentment, affliction, anger, and vexation—help them to become demons. That's why demons are always making trouble for people. They especially detest cultivators and see them as thorns in their flesh, so they try their best to destroy the cultivation of left-home people. They know that if a left-home person cultivates and be-comes a Buddha, they will lose one of their retinue, so they use all their might to ruin his cultivation. All left-home people should be careful and be on guard. Don't fall into the demons' snares. If you do, you may never get out. If Chan meditators fail to recognize states clearly, they will be taken in by the demons. This is called “catching fire and being possessed by a demon,” and it's extremely dangerous.
What are Buddhas? They are those who follow reason. Reason refers to cause and effect. What are demons? They are those who don't listen to reason. They don't heed cause and effect. To heed cause and effect is rational; not to heed them is irrational. The most obvious difference between Buddhas and demons is that while Buddhas are compassionate, demons are full of hate.