Soto Zen is a branch of Buddhism brought to Japan from China by a monk named Eihei Dogen. Dogen travelled to China in 1223, looking for a teacher, a practice, and an answer to a question about Buddhist practice and his life. 

It can seem that life poses us a question. Sometimes we can awkwardly wrap words around that question, sometimes we can't. Maybe we're not even aware of it, but we can still be driven to look for a sort of answer, a resolution to the themes and problems we see in ourselves and other people. Maybe that question arises as a response to suffering, or maybe it arises from a desire to do the best you can with your life, or a curiosity to find out what that might mean, what might be most important. This idea that life poses us a question is sometimes described as a koan in Soto Zen.

Descriptions of the life of the Buddha tell us that he had such a question. He would have described it as to do with the nature of human suffering and our relationship to it (Dukkha). He had a sense that it doesn't need to be like this, and that our deliberate involvement in it was a key. He found his answer, which has been described as an awakening, or enlightenment, and spent the rest of his life trying to show others how to realise this for themselves.

The Buddha passed on his teaching to his disciples, who passed it on to their disciples, until it eventually reached Eihei Dogen in the 13th Century AD.

Dogen's question was to do with the nature of Buddhist practice. He was taught that we all have innate enlightenment, innate 'Buddha Nature', and that there is nothing else to be gained, we already 'have'. If we don't gain enlightened nature because it's already innate in us, and never separate from anything we are or do, then do we even need to 'realise' this, why would that matter? What is the purpose of Buddhist practice?

Dogen found his answer through Zazen meditation, and taught that instead of meditation being a way to 'gain enlightenment', it can more usefully be described as itself a direct expression of our enlightened nature i.e. being enlightened. Zazen mind is enlightened mind, however dull and ordinary it might seem it is also miraculous, undivided. Sitting Buddha. 

In our practice we sit regularly in meditation, Zazen, to become increasingly familiar with that still, grounded mind of meditation, what that feels like. This allows us to ground our lives in a present moment awareness, in all our actions be more aware, more grounded, living closer to our innate Buddha nature you might say. Although we all have Buddha Nature often our actions come from confusion, selfishness possibly, distress, anxiousness, fear, desire. The more we meditate the more we can let these things come and go, and instead of being driven by them we can ground our actions and our lives in a deeper place, express our innate enlightenment. This liberates us from the uneasiness and emotional discomfort of being alive (Dukkha again).

In Soto Zen the practice of Zazen is central. It is the way we can come to know for ourselves what the Buddha was teaching us, and know why that is important. It's how we come to realise for ourselves our inner innate enlightenment.