The Four Nevers (Samaya)

The Bodhi Mind (bodhicitta) is the cause.
Great Compassion is the root and foundation.
Skillful means are the ultimate. — Mahavairocana Sutra

Through skillful means, the view of enlightenment is fulfilled in compassion towards other sentient beings.

For all sentient beings, be they Buddhas and Bodhisattvas, gods and demons, humans, hungry ghosts, and all of suffering the hells are primordial pure.

Thus they were born basically good, but, due to conditioning, all beings appear to be sentient.

Like a mirror in a sandstorm, the mind is subject to mental and physical negativities as a result of conditioning. No matter how much we wipe the mirror clean, the dust of worldliness soon shall settle on it.

Thus, the disciple commits to the Four Nevers:

• Never to abandon the True Dharma.
  
• Never to negate bodhicitta.
  
• Never to withhold or be selective of Buddhist teachings toward others.
  
• Never to cause any sentient being any harm.

Holding the True Dharma dear, the disciple consistently remembers the Buddha. Holding the bodhicitta dear, the disciple is caused by it to become Buddha. Holding the Buddhist teachings dear, the disciple shares the wisdom of the Buddhadharma that he has gleaned only with his fellow disciples. Holding life dear, the disciple refrains from harming any sentient being.

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Reference:

Samaya: http://en.wikipedia.org/wiki/Samaya