The link of connexion between the various Bodhisats in the future Buddha's successive births is not a soul which is transferred from body to body, but the karma, or character, which each successive Bodhisat inherits from his predecessors in the long chain of existences.
The ancient books, preserved in the Pali Pitakas, being mainly occupied with the details of Arahatship, lost their exclusive value in the eyes of those whose attention was being directed to the details of Bodhisatship. And the opinion that every leader in their religious circles, every teacher distinguished among them for his sanctity of life, or for his extensive learning, was a Bodhisat, who might have and who probably had inherited the karma of some great teacher of old, opened the door to a flood of superstitious fancies.
As the newer school did not venture so far as to claim as Bodhisats the disciples stated in the older books to have been the contemporaries of Gotama (they being precisely the persons known as Arahats), they attempted to give the appearance of age to the Bodhisat theory by representing the Buddha as being surrounded, not only by his human companions the Arahats, but also by fabulous beings, whom they represented as the Bodhisats existing at that time.
Amitabha, the Dhyani-Buddha of this trinity, soon began to fill the largest place in the minds of the new school; and Avalokite s wara, his Bodhisat, was looked upon with a reverence somewhat less than his former glory.