I get a little tired of Western Zennists translating the Chinese characters 平常心 as “ordinary mind,” and a few times with “everyday mind.” This strongly suggests that the path of Zen is mundane. By this I mean that you need not personally realize your true nature which is far from being mundane. We should not forget that the core of Zen is 明心見性, that is, illumination of Mind, seeing one's true nature.
A translation of the three Chinese characters 平常心 is not meant to convey the idea of the all-too-human empirical mind which is always engaged in emotion and thought. This term was meant to be used as something on par with “mind is the Buddha” which comes from the Sukhāvatīvyūha Sutra.
While Zen master Mazu of the Hangzhou school is given credit for the popularization of the term,平常心, it goes back earlier to Zen master Heze Shenhui where mind by him refers to what is transcendent rather than mundane. Shenhui’s mind is certainly not the ordinary, everday mind of humans.
Still, as regards mind, I believe Mazu believed as Shenhui did. I dare say that much of the problem owes to an improper translation. This seems to be the case if we look at a sermon by Mazu on this very subject. I will bracket “ordinary mind” using the equal sign followed by “natural mind.”
“If you want to know the Way directly, then [ordinary mind = natural mind] is the Way. What is an [ordinary mind = natural mind]? It means no intentional creation and action, no right or wrong, no grasping or rejecting, no terminable or permanent, nor profane or holy.”
This mind is akin to the perfected Buddha Mind. It is ineffable and original. It is unaffected, without artificiality, or strain. It is mind, naturally, before thought arises from it and becomes something determinate.
If we think of pure or natural water, it is water before some toxic chemical or dye is added to it. It has no smell to it. It is clear. The natural Mind, likewise, is pure and clear. It is free of thought. Having a natural Mind is being one with the Buddha-nature and the enlightenment of the Buddha.