Why did the Evil Dragon decide to leave for Good?

Seven hundred years after Sakyamuni Buddha entered Nirvana, an evil Dragon King Alina created all kinds of disaster in Northern India bringing great harm to the people. At that time there were 2,000 Great Arahants in the country who used their super natural power, trying to subdue and chase the dragon out but their efforts were in vain. Then there came a Great Honoured One Jeyata who went to the dragon pond. He stroke his fingers three times and said gently to the evil dragon, ‘Oh, Venerable Sir Worthy Goodness, please leave the country.’ Strange enough the dragon rose from the pond and flew away. The land was again in peace. Two thousand Great Arahants were very surprised. They asked the Honoured One, ‘Venerable Teacher Jeyata! We have fully utilized our super natural power but in vain. It is most unbelievable that the Honoured One has just struck the fingers three times and managed to send him back to the great ocean!’
The Honoured One Jeyata answered, ‘This is because of the merits and virtues in upholding the precepts. From the stage of a mundane man until now I have been upholding the precepts seriously. I respect my Teacher and I pay great attention in my pure karma of the body, mouth and mind even to the minute details. I treat the minor precept as important as the four heavy precepts. Because of our difference in the strength of precepts, you are unable to chase the evil dragon king.’
The dragon left because of its respect to an Arahant who paid equal importance in the practice of the heavy and minor precepts. His mind is in equanimity. The strength of his pure mind is greater than the strength of the super natural power of the other Arahants. So by upholding the precepts one’s mind will be pure and in equanimity and the strength far-surpasses the super natural power. This is the genuine practice of the Dharma. That is why the Buddha teaches us to take the precepts as our Teacher. With the adornment of precepts, we will advance in our practice and arrive on the road to great wisdom and great compassion. Without being asked the Dharma Protectors, the heavenly beings, the spiritual beings and even the Mara will bestow upon us their protection.
In the Nirvana Sutra, the Buddha says, ‘The cultivators who wish to see the Buddha Nature, to certify to Great Nirvana should uphold the pure precepts with a deep mind, a pure mind.’
The Buddha also says, ‘Those who transgress the precepts and study the sutras are the retinues of Mara. They are not my disciples. I do not even listen to their study of the sutra.’
Why does the Buddha not allowing people to study the sutras with no precepts? Let’s take the analogy of a knife. It can be used to cut up vegetables to prepare some delicious dishes. But if you give a baby the knife, he might cut himself or use it to harm others, to destroy many things. So those who do not uphold the precepts, who only sit in meditation, who read a sutra or who teach the dharma bring more harm to themselves and others. They are like the child who does not know how to use the knife properly. So without the guidance of precepts, the learning of sutras, the sitting in meditation or the teaching of dharma bring to the destruction of dharma because they do not possess the wisdom to utilize the Dharma Teaching.
“Cultivation is easy
But upholding the precepts is not easy.
With no precepts we are not different from the Mara,
When we keep the precepts our mind is at ease,
Pratimoksa will guarantee us to travel on the ship of liberation.
May you become a genuine bhikshu
May your mind be as pure as the vacant space and
With no taints of doing
And may you be adorned with lofty virtue
That resembles the green lotus.
With your cultivation and understanding
You will be the Great Dharma Ship
That ferries living beings across the seas of sufferings.”

The teaching content and poem was translated from the Dharma teaching of Venerable Master Shi Miao Xiang, the Abbot of Da Bei Si, Haicheng, Liaoning in China, in the exhortation of the Sangha