Although there are immeasurable Buddhas,
there is only one goal of Buddhahood attained by them,
and one complete Dharma based on Bodhicitta realised.
A young student in a Dharma class asked me three interesting questions…  Why are there so many Buddhas and Bodhisattvas? (She was probably confused by their many identities and related teachings?)  Why is there not just one fully enlightened being? (She probably felt this would make learning Buddhism easier?)  Is there any difference between mindfulness of one Buddha or Bodhisattva versus another? (She probably wanted to streamline her mindfulness practice?) Here are my answers…  It is perfectly natural that there are immeasurable Buddhas and Bodhisattvas. As Buddhahood is the result of perfecting the Bodhisattva path of perfecting compassion and wisdom, and since there are countless beings in innumerable worlds who aspire to walk this noblest of paths in the past, present and future, there are of course many Bodhisattvas and Buddhas. That there are many of them is actually very inspiring and encouraging good news, because this reminds us that we too can become like them. The historical Shakyamuni Buddha also predicted the eventual Buddhahood of many of his disciples.
 Because there is only one state of complete and unsurpassed enlightenment, what every fully enlightened being realised is exactly the same. In this sense, they become one with the universal ‘body of truth’ that pervades all time and space. This form of their existence is called the Dharmakaya. Seen from this perspective, there is indeed only one common collective ‘pool’ with the essence of perfect enlightened compassion and wisdom. The question might still remain, as to why the fully enlightened ones do not thereafter simply present themselves as one for our ‘convenience’. As the Dharmakaya is as if a dynamic ever-expanding collective, it is important that there are many individual beings presented in the Buddhist teachings, who are or become part of it. This reminds us to emulate their example, to align more deeply with our Buddha-nature. Despite being of the Dharmakaya, Buddhas continue to retain their individual identities to skilfully manifest to beings with specific karmic affinities, to effectively guide more with the Dharma.
In fact, ancient Buddhas even re-manifest as Bodhisattvas out of endless compassion to guide beings still in suffering, and to exemplify the path to Buddhahood. Guanyin Bodhisattva is one of them, who already attained Buddhahood many kalpas ago. How very moving! As in her case, Bodhisattvas can, also out of great compassion, choose to more strongly personify certain virtues, so that, for ease of focus, we can see them as shining perfect examples of the qualities we aspire to cultivate. For example, Guanyin Bodhisattva represents the perfect compassion of all Buddhas, which is possible since she is already a Buddha, one with the collective compassion of all Buddhas in the Dharmakaya. Since she is a Buddha, she is of course not lacking in other virtues such as wisdom. Likewise, all other great Bodhisattvas, even if they personify some virtues less, do not lack them.  Wholehearted mindfulness of any one Buddha or perfect Bodhisattva we feel the greatest affinity to thus connects us to the Dharmakya’s collective compassion and wisdom without difference, aligning us to the one same goal of Buddhahood, as according to our spiritual aspirations.
As we are scatter-minded, even in mindfulness of Buddhas,
out of compassion, Shakyamuni Buddha taught the most
about mindfulness of Amitabha Buddha (Amituofo),
so as to rein in our wandering minds.
Understanding Amituofo Via The Amitabha Sutra (10th Run)