Buddha nature is mostly misunderstood by Theravadist and some Mahayana practitioners.
The mistake is they think Buddha nature is the potential (seed) that everyone including animal, ghost, anyone can become a Buddha.
Everybody knows that everyone can become a Buddha. There is no need this kind of statement.
However, what is shocking in the teaching in Buddha nature is Maitreya said everyone is actually already a Buddha. But they don't know it.
This is a very shocking news actually.
How can someone is he is already a Buddha, but he doesn't know about it?
It is impossible! This is the argument used by the opponents of Buddha nature.
Up to this point it has to be clear that Buddha nature is not the seed or potential. But it tells you straight away you are Buddha now, but you don't know. Sometimes, they call it you are sleeping Buddha.
The argument that is proposed by the opponents to reject Buddha nature is actually very weak.
How can someone is already a Buddha cannot know he is a Buddha?
Do you remember Copernicus who tell you Sun the centre of the orbit in 16th century?
Copernicus tell the church the sun is the centre of the orbit?
If sun is the centre of the orbit, how can everyone cannot know it?
This is exactly similar with the argument used to reject Buddha nature.
If you are already a Buddha, how can you don't know it?
Why we are already a Buddha?
Please see yourself when you do a meditation.
When we do a meditation, the deeper you get the deeper you find out that your true nature is actually impermanent and Anatta.
If your nature is not a Buddha, but evil, the more you silent and look directly in yourself, the more evil nature wil come out.
If life is permanent and has self, when you sit and meditate to look deeper in yourself, permanent and self (atta) will getting stronger and stronger. But in reality, this is not the case.
This is the first proof that in yourself right now, you are actually impermanent and Anatta. If you can see that, it is because you have a concept that cover you to believe you are permanent and having self.
This is exactly similar with Copernicus that tell the church, look sun is the centre of the orbit. But all church membered didn't believe him, because all of them are covered by the concept that the earth is the centre of the orbit.
The second proof that you are already a Buddha is seen by how Buddha suggest you to meditate.
All Buddhist master always suggest you to look into you.
All Theravada master, Mahayana master, they go to the cave or in the private place just to look inside themselves. They don't bring instruments, or medicine or anything that if you apply this medicine or use that machine, you thn become a Buddha.
But what happen is, they don't use anything.
They just ponder inside without anything. Until they discover yes, actually my breathing is impermanent. Yes, actually my breathing has no self. Yes, actually this feeling has no self. Yes, this body is impermanent and has no self.
Why such an impermanent and no self reality, I can never know?
They have been already like that and why I never know? Why only today after instant in the cave and look inside I just know?
This kind of reality has been with me since beginningless time. Why I cannot know something which is already like this until this very moment?
There is no one in this world saying - today I successfully make myself impermanent and make myself Anata.
There are many people who think that Buddhahood is a kind of making instead of realizing.
Many people actually think that to become a Buddha is like to make a cake. So what happen to them? They travel this place and that place. They try to find this method and that method. They think as if by doing this or doing that, they can become a Buddha. They think that to become a Buddha is like to make a cake.
Until unlimited eons, if they try in this way, buddhahood is far from them.
This is well explained by Buddhist master that the diamond is in your pocket, but you look all over the place, traveling here and traveling there, asking this method and that method, to find the diamond. But there is one thing you never do, which is checking your pocket.
Why Buddha nature is extremely important, because this teaching tell you straight away that what you are looking for is not outside, it is already there inside you. You just need to find it.
However, if Maitreya never tell you that inside you is your buddhahood, what is the point to look inside?
Nagarjuna said, if inside the ground, there is no diamond, you search there until you die, you won't find it
But if inside that ground has a diamond, it is worth to search there.
Similarly, if you are not impermanent and Anatta since beginningless time, there is no point for you to look into yourself. Because that effort is futile - you are just trying to find a soil without a diamond.
But, if you are already impermanent and Anatta, even you can't see it right now because you are covered by concept of permanent and self, please trust your Buddha nature.
Look inside you, you will definitely find it.
Buddha nature is in you right now.
You don't believe it, that is find.
But, only looking inside you, you can uncover the impermanent and anatta beyond concept.
You can read all MN, AN, all Mahayana Sutta, your buddhahood is simply not in those paper. You will just find this word impermanent and anatta printed in the paper.
Like you find a word of diamond print in the paper. But the real diamond in already in you right now.
Just like a sun is the centre of the orbit, it doesn't mean you can know it.
Just like you are already a Buddha, it doesn't mean you can know it.
After you study in the school, you realize sun is the centre of the orbit. You realize what is already there. You can't create it anyway.
After you follow 8 noble paths, you realize your Buddha nature. You realize what is already there. You can't create Buddha anyway. You can just realize what is already there through 8 noble paths.
I am not here nor there.
I am not right nor wrong.
I do not exist neither non-exist.
I am not I nor non-I.
I am not in samsara nor nirvana.
To All Buddhas, I bow down for the teaching of emptiness. Thank You!