The similarities between the Tendai school's "Hongon" doctrine and Vedanta during the time of Dogen are interesting.

According to "Rethinking Japanese Buddhism (P89)," the Tendai school's "Hongon" doctrine, while based on the ideas of Chinese Tendai scholar Zhiyi, also included a uniquely Japanese concept that one doesn't need to practice because "since you are already enlightened, you are already a Buddha as you are." Dogen questioned this and left Mount Hiei.

This kind of idea, that one doesn't need to practice, or that "understanding" is enough, seems similar to the "Hongon" doctrine and the Indian Vedanta. In reality, they are quite different, but they may appear similar, and one might interpret them in a way that resembles the "Hongon" doctrine.

The "Hongon" doctrine is quite extreme, but it is somewhat similar to the concept of "Atman" in Vedanta.

Atman is the essence of a human being. According to Vedanta, what ordinary people think of as themselves is the "ego" (ahamkara), which is the interaction of memory and intelligence (chitta). Atman is the true self, and is also translated as "true self."

The idea that Atman is the true self, and that this true self already knows everything, is complete, and is eternal, overlaps with the concept of the ego (ahamkara) as the interaction of memory and intelligence (chitta), which is a kind of illusion. However, if one mistakenly equates the concept of Atman with the concept of the ego, one might conveniently interpret it as "I (the ego) am already enlightened, so I don't need to practice." This is because one does not understand the original concept and misinterprets it for convenience.

In reality, it is Atman that does not need practice. The ego, which is called "Jiva" in Vedanta, is the self that lives with the feeling of being a phantom of the self, memory, and intelligence (chitta). For Jiva, normal practice is necessary.

In some schools, these concepts are mixed up, so there are times when the idea of "no practice" and the idea of "practice is necessary" are mixed together. In such cases, the word "practice" is often replaced with "understanding" to express the half-understood concept. However, it is better to clearly distinguish between Atman and Jiva.

In some schools, the idea that practice is not necessary for Atman is somehow mixed with the concept of Jiva, and it is said that Jiva can become aware of Atman and achieve liberation from reincarnation (moksha) simply by understanding. However, from the perspective of Jiva, that is still practice. However, some schools inexplicably mix the concepts of Atman and Jiva, and say that "since practice is an action, action is not necessary for Atman."

Indeed, practice is not necessary for Atman, but all actions are actions for Jiva, and even those actions are necessary for Jiva to approach Atman. However, some schools say that such practice is not necessary, and yet, when you actually see what those schools are doing, you can see a strange sight where they are doing things that seem like practice, even though they say it is not practice.

In this way, mixing Atman and Jiva leads to unnatural expressions. It is better to clearly distinguish between Atman and Jiva.

It is good that Atman does not need practice and is already enlightened. However, it would be clearer to say that practice is necessary for Jiva.