Corresponding to the 84,000 (countless) kinds of minds and natures of living beings, there arise 84,000 (countless) Dharma doors (methods of practice) that have form and appearance. Such Dharma doors, which have tangible form, can generally be divided into the Chan, Teaching, Vinaya, Pure Land, and Esoteric Schools. If divided more finely, they are more than 84,000 in number. Even if the most intelligent person were to devote his entire life's energy to studying them, probably he would not be able to completely master them all. That's how the idea of “Deeply entering one door” came about.
eeply entering one door” literally means to select one of the 84,000 Dharma doors and study and understand it in depth. Which is the best door? Which is the most convenient and effective, the most ultimate? Each person should make his own selection according to his personal inclinations and needs. There are people who recite the Buddha's name or a certain mantra all their lives. Others spend their lives studying the Sutras and Shastras. Others focus on meditation or moral discipline. Each person claims their own choice is the right one, and others’ choices are wrong. No matter which sect it is, “when they are in it, they advocate and support it. When they leave it, they scorn and slander it.” All kinds of sectarian views and factional differences arise. This is truly a case of attachment to appearances! And so it's said, “Those who see only the appearances of things are bound to become attached to appearances.”
When a wise person views the situation, he sees that people are only drawing boundaries amongst themselves and indulging in vain afflictions with their petty feuds. “One root has ten thousand ramifications.” “Ten thousand dharmas return to one.” “Others’ experiences can be lessons for us.” “When one Sutra is understood, all Sutras are understood.” No matter which Dharma door you cultivate, if you hope to succeed, you must concentrate single-mindedly. That is, you must focus your mind on one thing. If you can't fulfill this requirement, you won't succeed with any Dharma door. If you don't believe it, I invite you to search the past and present and all the ten directions. You will not find any person who has ever successfully accomplished a task or studied a Dharma when his mind was on something else.
Therefore, although there are formally many different kinds of Dharma doors, in terms of the mind, there is only one kind--that of single-minded concentration. If a cultivator only makes vain discriminations about form and appearance, then even if he selects one door to enter, he cannot enter it deeply. He must advance spiritually and broaden his outlook before he can make a proper choice. Then, focusing his mind and attention and clearly recognizing his goal, he must put forth his full strength. Only then can he really enter deeply and taste the wonderful flavor of ghee. At that point, the one and the many are unobstructed and everything mutually interpenetrates. There is no place where he is not at ease. Therefore, although there are many Dharma doors, we must be able to deeply enter one door. And the spirit of deeply entering one door lies in focusing the mind on a single point.