Geshe Rabten Rinpoche
The Graduated Path to Liberation

Yana is not the carrier or what is carried-it is the carrying. Thus Hinayana means "carrying the smaller load," and Mahayana, "carrying the great load."
Hinayana practitioners are those who find samsara unbearable and want to escape from it into the state of nirvana. They help others enormously by renouncing the world and striving to obtain freedom, but their main thought is personal liberation from samsara. An arhat-one who has completed this path of personal liberation-has many spiritual powers, and can give spiritual teaching and aid to many beings, but still has to remove jneyavarana. The attainment of nirvana will prove not to be sufficient and the arhat will then have to enter the bodhisattva path and progress through the ten levels to the final, complete buddhahood.
Those who practise Mahayana also renounce samsara and want to escape from it. But because they identify with all other beings in samsara, Mahayanists do not want merely personal liberation. Through their great concern for others, Mahayanists' all-motivating wish is to give complete happiness to all beings. They understand first that all beings in samsara-insects, devas and the rest-are equal in that they all want happiness and do not want suffering. They also perceive that none of these beings has the satisfaction of complete happiness. For this reason, they develop the great wish to take all beings out of suffering. This wish, which is also a kind of caitta, is called mahakarunika, "the great compassionate one." Mahayana practitioners realize that all beings in samsara, though they may have transitory happiness, do not have true, lasting, happiness.
The next wish, that of giving all beings the ultimate happiness of buddhahood is called mahamaitreya, "the great wish of active love." These wishes are stronger than the dissatisfaction of the Hinayana follower. Before this stage of aspiration is reached, there are many other practices that have to be developed so that Mahayanists can fully realize the suffering of beings.
At first they want to bring all beings to enlightenment without any help. This is called adicinta, "the first thought." Then, when they examine themselves to see if they have enough power to do so alone, they find that the same defilements that other beings have exist within themselves as well. Thus they try to find who does have the power to help others in this way. Through this they find that only a buddha can do so, and develop the wish to reach the buddha stage quickly. This is bodhicitta , "the mind dedicated to enlightenment."
When one has practised this a great deal, mahakarunika, mahamaitreya, adicinta and bodhicitta become part of the person's very nature. At this point the practitioner becomes a bodhisattva, though not yet an arya-bodhisattva-a very advanced bodhisattva, who has seen emptiness clearly. When the practitioner reaches the high state of a bodhisattva, all the devas pay respect. Once bodhicitta has arisen, the seed of Dharma will continue to grow whether the person is awake or asleep, and even very harmful karma can be prevented from ripening.
Usually, people can remove mental defilements only by meditation on emptiness. Bodhicitta makes meditation on emptiness much more powerful. When a soldier is fighting an enemy he needs to use his weapon, but he also needs to have good food; bodhicitta is like this food.
To reach the final goal we need two instruments: prajna (wisdom), and upaya (right means), which contains both compassion and compassionate activity. Mahakarunika, mahamaitreya, adicinta and bodhicitta are all included in upaya. Prajna is seeing things as they really are. A bodhisattva must have both of these. Arhats, who have completed the Hinayana path, are out of samsara and have attained the lowest level of nirvana, are strong in prajna-in the realization of emptiness-but weak in upaya. They have compassion (karuna), but not the great compassion of mahakarunika. They have active love (maitri), but not mahamaitreya. The main difference between their path and that of the Mahayana is on the side of upaya. Eventually, arhats will have to develop it.
Pandit Shantideva, in his Bodhicaryavatara, mentioned all the different virtues of bodhicitta, for those interested in knowing more about the mind dedicated to enlightenment.