Among the followers of the Buddha, including lay practitioners, there were Buddhas of the past and great bodhisattvas. They manifested as ordinary people but were actually saints. The Essentials says: “The sound-hearers were listed first because they assumed the appearance of one who has renounced the world, because they always followed the Buddha, and because the spreading of the Dharma depends on the Sangha.” The sound-hearers always appeared as monastics who had renounced the world, but the bodhisattvas did not always appear as such. Most bodhisattvas had the appearance of lay people. The bodhisattvas did not always follow the Buddha but the sound-hearers did because they had not completed their study. The sound-hearers were bhiksus, and bhiksus were students of the Buddha who had not completed their study and thus needed to constantly follow the teacher. The bodhisattvas had completed their study and could thus leave the teacher’s side.
There was no set place for the Buddha to teach. Where did he teach? In a forest, by a river, or near a brook. There were no buildings or any facilities. They slept under the trees and ate one meal a day before noon. They lived in the wilderness. When the kings and ministers heard about the Buddha, they were full of admiration and sincerely wanted the Buddha to live in their countries to teach. The Buddha accorded with the conditions and went wherever people invited him. He was able to spread his teachings to a large area and to truly benefit all beings. The bodhisattvas also went everywhere to teach. Because there were many places where the Buddha was invited to teach and because he could not go to all of them, sometimes the sound-hearers were sent out to teach on his behalf. After teaching for a period, the students would come back, and other students would be sent.
~ Based on Ven. Master Chin Kung's 2003 lecture series on the Amitabha Sutra