Why do we have enlightened Masters who descend to this world life after life to save sentient beings? Even though all beings have the Buddha nature, we wouldn’t be able to become Buddhas without being given the key to enlightenment from a living Buddha. Thus, Buddhas have to come back life after life. However, sentient beings experience many obstacles during their lifetimes. They bear not only their own karma, but also that of their ancestors and the collective karma of their families, districts, and countries. This karma is so heavy that they are not able to go and look for a Buddha through their own effort. For this reason a Buddha has to give lectures in order to preach the Dharma.
If a Buddha did not possess a physical body, other beings would not be able to recognize him. Likewise, the Buddha would not be able to pass down the Dharma to other humans. The levels of humans are different from those of Buddhas and Bodhisattvas, so heart-to-heart transmission is necessary. Once the mindset of humans changes over time and reaches the level of Buddhas and Bodhisattvas, they can start to learn from Buddhas and Bodhisattvas. When Buddhas and Boddhisattvas come to this world, they become ordinary people right at birth and have to take time to reach Buddhahood. Such a process is really painful for the Buddhas and Boddhisattvas. Indeed, they come down to help us out of their immense compassion.