Bodhisattvas
Much as the Theravada student strives to become an arhat — a spiritually enlightened individual — so the Mahayana student strives to become a bodhisattva. A bodhisattva is a person who has already attained enlightenment, or is ready to attain enlightenment but puts off his own final enlightenment in order to re-enter the cycle of samsara and save all sentient beings. A bodhisattva is the ultimate in compassion, and Mahayana Buddhists believe that enlightenment can be attained not only by striving individually but also by helping others to achieve enlightenment as well.
Every bodhisattva resolves to realize the Four Great Vows:
Sentient beings are numberless; I vow to save them.
Desires are inexhaustible; I vow to put an end to them.
The dharmas are boundless; I vow to master them.
The Buddha Way is unattainable; I vow to attain it.
Bodhisattvas willingly seek to be reborn into the endless cycle of samsara so that they can constantly help others toward their own enlightened state. They need wisdom so that they can discern how to help others toward nirvana. Bodhisattva's employ compassion and love for all beings.
They use upaya (skillful means) to accomplish their aim of benefiting all sentient beings. Inherent within skillful means is wisdom — the ability to discern how to help each sentient being toward enlightenment. Wisdom heart is referred to as bodhicitta — the quality that allows them to be open to the suffering of others. Therefore, someone who desires to become a bodhisattva will develop and then generate bodhicitta. As you can see from the concept of the bodhisattva, Mahayana traditions rely more explicitly on concepts of rebirth, whether taken literally or metaphorically.
In addition to generating bodhicitta, the bodhisattva also strives for the Six Perfections:
Concentration (meditation)
Giving
Morality
Patience
Persistence
Wisdom
Without the explicit commitment to rebirth for the benefit of all sentient beings, Mahayanists looked down upon Theravada practitioners and called them shravakas (“listeners”). Being an arhat (an enlightened one) is not enough; one must strive to become a buddha. Without that commitment, Theravada appears to honor the letter of practice (“well, the Buddha didn't say I had to take rebirth”) versus the spirit of the practice — a wish to benefit everyone. If one does not believe in rebirth, this distinction becomes moot, but in the Buddha's day these were very much living arguments.
Since there haven't been any more buddhas in the past 2,500 years, the argument likewise seems moot. A bodhisattva can also be understood as a future Buddha. If you take the bodhisattva vows, you undertake the arduous journey towards not just enlightenment but buddhahood. Good luck! The bodhisattva trucks in compassion and wisdom, and these virtues are more explicitly pursued and codified in the Mahayana traditions.
Three Bodies (Trikayas)
Mahayanas believe that buddha-nature appears in three different forms. These bodies are the forms that the Buddha or buddha-nature take. This is known as the Three Body Doctrine of compassion. As elsewhere, these bodies can be interpreted symbolically as well as literally. The three forms are:
Nirmanakaya (emanation body) refers to the historical Buddha as he embodied the truth of the dharma in a perfected form. This is reflected in the story of Vakkali, who called for the Buddha when he was sick. The Buddha told him, “What good is the sight of this putrid body to you? Vakkali, the one who sees the dharma sees me; the one who sees me, sees the dharma.” The Buddha and the dharma are one in the same (and you will often see this conjunction: buddhadharma).
Sambhogakaya (bliss body) is the idealized form of the Buddha. This “body” of the Buddha is not limited to its physical form and, in traditional thought, would occupy different realms or represent different states of consciousness. This body is experienced through intensive meditation.
Dharmakaya (truth body). According to Buddhist scholar John Peacock, the “Dharmakaya is synonymous with ultimate truth and is seen as being totally transcendent and unchanging.” The Dharmakaya refers to the approximation the human mind can sometimes make with reality. This body is enlightenment.
