As I study both the exoteric and the esoteric schools of Buddhism, they maintain that human beings are endowed with Dharma-nature by birth. If this is the case, why did the Buddhas of all ages — undoubtedly in possession of enlightenment — find it necessary to seek enlightenment and engage in spiritual practice?

As quoted in Eihei Dogen, Mystical Realist (2004) by Hee-jin Kim