I am very glad to be here on the day Buddha attained enlightenment under the Bo tree. When he attained enlightenment under the Bo tree, he said, "It is wonderful to see Buddha nature in everything and in each individual!"
What he meant was that when we practice zazen we have Buddha nature, and each of us is Buddha himself. By practice he did not mean just to sit under the Bo tree, or to sit in the cross-legged posture. It is true that this posture is the basic one or original way for us, but actually what Buddha meant was that mountain, trees, flowing water, flowers, and plants--everything as it is--is the way Buddha is. It means everything is taking Buddha's activity, each thing in its own way.
But the way each thing exists is not to be understood by itself in its own realm of consciousness. What we see or what we hear is just a part, or a limited idea, of what we actually are. But when we just are--each just existing in his own way--we are expressing Buddha himself. In other words, when we practice something such as zazen, then there is Buddha's way or Buddha nature. when we ask what Buddha nature is, it vanishes; but when we just practice zazen, we have full understanding of it. The only way to understand Buddha nature is just to practice zazen, just to be here as we are. so what Buddha meant by Buddha nature was to be there as he was, beyond the realm of consciousness.
--from Zen Mind, Beginner's Mind by Shunryu Suzuki