|Gandhara Maitreya Buddha (asianart.org)|
This assumption is not entirely correct, for the Theravāda tradition has absorbed the bodhisattva ideal [and many Mahayanists in the past and now would indeed strive for the stages of enlightenment] into its framework and thus recognizes the validity of both arhatship and buddhahood as objects of aspiration.
It would therefore be more accurate to say that the arhat ideal and the bodhisattva ideal are the respective guiding ideals of Early Buddhism [Sarvastivada and the Hinayana schools, of which Theravada is not one but gets called one because of its age and its keeping with early ideals and teachings] and Mahāyāna Buddhism.
"Early Buddhism" is not the same thing as Theravāda Buddhism that exists in the countries of South and Southeast Asia. It refers to the type of Buddhism embodied in the archaic Nikāyas [collection, division, volume, assemblages of sacred texts] of Theravāda Buddhism and in the corresponding texts of other schools of Indian Buddhism that did not survive the general destruction of Buddhism in India.
It is important to recognize that these ideals, in the forms that they have come down to us, originate from different bodies of literature stemming from different periods in the historical development of Buddhism.
If we fail to take this fact into account and simply compare these two ideals as described in Buddhist canonical texts, we might assume that the two were originally expounded by the historical Buddha himself. Then we might suppose that the Buddha -- living and teaching in the Gangetic plain in the fifth century B.C. -- offered his followers a choice between them, as if to say: "This is the arhat ideal, which has such and such features, and that is the bodhisattva ideal, which has such and such features. Choose whichever one you like."
- There is also a third model of Buddhist spiritual life, that of the pacceka-buddha (Sanskrit pratyeka), which is similar in many respects to the disciple arhat, except that the disciple arhat attains enlightenment under the guidance of a teaching buddha, and other gains enlightenment without any outside guidance [after an incredibly long time and a great deal of effort and uncertainty with no ability to teach the Path to others]. Otherwise, the combination of qualities that constitute this type is essentially the same. In the literature of the Buddhist systems, we often read of three types of fully enlightened ones -- disciples ("hearers," Pali sāvakas), nonteaching (pacceka) buddhas, and supremely or perfectly enlightened teachers (sammā sam buddhas, Sanstrit śrāvakas, pratyeka-buddhas, and samyak sam buddhas). And of the three vehicles (yānas) that lead to these attainments.
The most archaic Buddhist texts -- the Pali [an exclusively Buddhist language] Nikāyas and their counterparts from other early schools (some of which have been preserved in the Chinese Āgamas and the Tibetan Kanjur) -- depict the ideal for the Buddhist disciple as the arhat.
The Mahāyāna sūtras, composed a few centuries later in a Buddhist hybrid Sanskrit, depict the ideal for the Mahāyāna follower as the bodhisattva. Now some people argue that because the arhat is the ideal of Early Buddhism, while the bodhisattva is the ideal of later Mahāyāna Buddhism, the Mahāyāna must be a more advanced or highly developed type of Buddhism, a more ultimate teaching compared to the simpler, more basic teaching of the Nikāyas.
That is indeed an attitude common among [average or unlearned] Mahāyānists, which I will call "Mahāyāna elitism." An opposing attitude common among conservative advocates of the Nikāyas rejects all later developments in the history of Buddhist thought as deviation and distortion, a fall away from the "pristine purity" of the ancient teaching. I call this attitude "Nikāya purism."
Taking the arhat ideal alone as valid, Nikāya purists reject the bodhisattva ideal, sometimes forcefully and even aggressively.
I have been seeking a point of view that can do justice to both perspectives, that of the Nikāyas and the early Mahāyāna sūtras, a point of view that can accommodate their respective strengths without falling into a soft and easy syncretism, without blotting out conceptual dissonances between them, without abandoning faithfulness to the historical records -- yet one which also recognizes that these records are by no means crystal clear and are unlikely to be free of bias.
This task is difficult. It is much simpler to adopt either a standpoint of "Nikāya purism" or one of "Mahāyāna elitism" and hold to it without flinching. The problem with these two standpoints, however, is that both are obliged to neglect facts that are discomforting to their respective points of view.