In Mahayana Buddhism, the ideal of practice is to become a bodhisattva who strives to liberate all beings from the cycle of birth and death. The Bodhisattva Vows are vows taken formally by a Buddhist to do exactly that. The vows also are an expression of bodhichitta, the desire to realize enlightenment for the sake of others.
The exact wording of the Bodhisattva vows varies from school to school. The most basic form is:
May I attain Buddhahood for the benefit of all sentient beings.
A passionate variation of the vow is associated with the iconic figure Ksitigarbha Bodhisattva --
"Not until the hells are emptied will I become a Buddha; not until all beings are saved will I certify to Bodhi."
The Four Great Vows
Beings are numberless, I vow to save them
Desires are inexhaustible, I vow to end them
Dharma gates are boundless, I vow to enter them
Buddha's way is unsurpassable, I vow to become it.
These four vows encompass all of Buddhism.
In his book Taking the Path of Zen, Robert Aitken Roshi wrote (page 62),
I have heard people say, "I cannot recite these vows because I cannot hope to fulfill them." Actually, Kanzeon, the incarnation of mercy and compassion, weeps because she cannot save all beings. Nobody fulfills these "Great Vows for All," but we vow to fulfill them as best we can. They are our practice.
Zen teacher Taitaku Pat Phelan said,
When we take these vows, an intention is created, the seed of an effort to follow through. Because these vows are so vast, they are, in a sense, undefinable. We continually define and redefine them as we renew our intention to fulfill them. If you have a well-defined task with a beginning, middle, and end, you can estimate or measure the effort needed. But the Bodhisattva Vows are immeasurable. The intention we arouse, the effort we cultivate when we call forth these vows, extends us beyond the limits of our personal identities.
Tibetan Buddhism: The Root and Secondary Bodhisattva Vows
In Tibetan Buddhism, the term "Bodhisattva Vows" usually refers to two sets of vows, sometimes called the "root" or "secondary" vows, or the root or secondary downfalls. These are lists of behaviors that a bodhisattva should avoid, many of which are also found in the Precepts.
Shantideva was a monk and scholar who lived in India in the late 7th to early 8th centuries. His Bodhicaryavatara, or "Guide to the Bodhisattva's Way of Life," presented teachings on the bodhisattva path and the cultivation of bodhichitta that are remembered especially in Tibetan Buddhism, although they also belong to all of Mahayana.
Shantideva's work includes a number of beautiful prayers that also are bodhisattva vows. Here is an excerpt from just one:
May I be a protector to those without protection,
A leader for those who journey,
And a boat, a bridge, a passage
For those desiring the further shore.
May the pain of every living creature
Be completely cleared away.
May I be the doctor and the medicine
And may I be the nurse
For all sick beings in the world
Until everyone is healed.