Are Buddhism's Oneness and Ten Realms Conflicting with Each Other?

Buddhism says the universe is One. Buddhism also says the universe contains Ten Realms. Are they conflicting with each other?

Are the ice and water two or one? Judging by their forms they are two. Judging by their essence they are one. Are they conflicting with each other?

Probably not, as we consider them as just two different points of view. It's a matter of perspective. Same to Buddhism's Oneness and Ten Realms - they are also a matter of perspective, and they are both reality.

The key is this: The universe is one, but forms and manifestations are many. Just like the liquid called H2O can appear in the form of water, ice, snow, or vapor - all look different - the Oneness can manifest itself in different forms too. Our knowledge has told us that water and ice and snow are all essentially the same. But what if it's equally true, although our knowledge hasn't been able to tell us, that Buddha and human beings and animals are also essentially the same?

Put it in a different analogy. If the Oneness is a calm and peaceful ocean, then the Ten Realms are waves and surfs that arise from and dissolve into the ocean. Waves and surfs create different images that we observed, but they are essentially no different from the ocean itself - they are all water. So the Diamond Sutra is true in saying "Buddha is sentient beings and sentient beings are Buddha." The Heart Sutra is also true in saying "Form is emptiness and emptiness is form." Both for this reason.

Buddhism says that everyone has the innate Buddha-nature that is as pure as the one of Buddha. Just like a peaceful and calm ocean, without any disturbance. The disturbance - ripples, waves and surfs - are our cravings arising from our five senses. Attachment of this sort includes craving, anger, infatuation, arrogance and suspicion. These disturbances may appear pleasurable for a while - just like waves and surfs seem appealing and colorful than the static ocean - but they are only temporary. The anger waves may put your surfboard of career or other endeavor a bit further, they are bound to be huge and devouring when they come back against you. How often the anger seems to be a justified weapon in justifying ourselves? But how more often our life crumbles also because of anger?

Meditation, one way to look at it, is to calm the disturbances and reveal the original calm and undisturbed one - the Buddha-nature. Since there is no separate entity called the Buddha-nature, searching for it is always a vanity. Only when all the disturbances are gone will you discover it. After all, the ocean is always there - just that whether or not you can see it.