That the self advances and confirms the myriad things is called delusion. That the myriad things advance and confirm the self is enlightenment. - Dōgen

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?

"Kind mind" is parental mind. Just as parents care for their children, you should bear in mind the three treasures. Even poor or suffering people raise their children with deep love. Their hearts cannot be understood by others. This can be known only when you become a father or a mother. They do not care whether they themselves are poor or rich; their only concern is that their children will grow up. They pay no attention to whether they themselves are cold or hot but cover their children to protect them from the cold or shield them from the hot sun. This is extreme kindness. Only those who have aroused this mind can know it, and only those who practice this mind can understand it. Therefore, you should look after water and grain with compassionate care, as though tending your own children.

Such a practice requires exerting all your energies.5 If a man entrusted with this work lacks such a spirit, then he will only endure unnecessary hardships and suffering that will have no value in his pursuit of the Way.