As it is written in the Maha Prajna Sutra, it is necessary:

1. To concentrate our mind on the cognition of enlightment (the perfect wisdom)
2. To focus on the thought of great compassion; and
3. To learn the skillful means of emptiness (the universal reality behind all phenomena)

This sutra [Maha Prajna Sutra] stresses the importance of learning all the methods of practice for bodhisattvas. While all methods are no more than ways to cultivate goodness and wisdom, they should comply with these three essentials. The ultimate goal of all practices is to attain perfection in these three virtues.