To investigate the ultimate Ch’an, you should fulfill four conditions. If these conditions are met, it is possible to realize the highest aims of Ch’an. Short of this, your path is uncertain, and progress is difficult. But these conditions must come spontaneously out of your practice. Certainly a master can’t force them on you or even give them to you. Arising from within, they can be fulfilled more quickly. A master can only lead a disciple onto the Path. The disciple must follow the Path himself. I can only tell you what these requirements are and why they are necessary. The rest is up to you.
When you enter the Path, if you are full of zeal, these conditions arise very naturally. But don’t expect them all at once. You must first begin to practice. As you make progress, they will gradually, or in some cases, quickly, be fulfilled. Much depends on your causes and conditions. Therefore at the beginning of a retreat I do not mention these requirements. I will only talk about them when I see that people are physically and mentally ready to investigate Ch’an.
What are these four conditions? The first is Great Faith; the second is Great Vow; the third is Great Determination; and the fourth is Great Doubt. Great Faith always arises first, followed by Great Vow, and then Great Determination. When there is Great Determination, it is then possible to generate Great Doubt. This is their natural sequence. But Great Doubt is not the ordinary doubt of disbelief. Only when there is Great Faith is it possible to have Great Doubt. Were you to have ordinary doubt at such a time, it could only be a sort of suspicion or non-belief, the opposite of faith. That kind of doubt is not a condition of practice: it is an obstacle.
— Getting The Buddha Mind by Master Sheng-Yen (page 17-18)