What is that which is the cause of liberation? Passionless is the answer... And what is that which is the cause
of passionlessness? Repulsion is the answer...And what is that which is the cause of repulsion? The knowledge and the vision of things as they really are is the answer (Yathabhutananadassanan). --Samyuttanikaya PTS II, p. 30.
"Seeing things as they are" is the answer for nirvana. Seeing everything just as it is without
differentiation, without attachment -- Spontaneous. Zen Buddhism emphasizes the Buddha nature by saying that everybody can become Buddha. Seeing the Buddha nature while becoming Buddha. Taoism emphasizes Spontaneous by saying that God is over men, ultimately, the Nature/Spontaneous is above God. So the most important thing is Spontaneous. Spontaneous can be used to treat our daily life. You have no differentiation on everything, so you are serene, you are happy!