With meditative concentration, deliberation becomes clear and penetrating

If your train of thought is not clear enough, it means you lack meditative concentration (samādhi), and you should cultivate more concentration to make your thinking clearer. When the power of concentration is insufficient, the mind consciousness's thinking cannot follow a single main thread, and it will become distracted in all directions, without focus. It is like qi channels not running along a single line, but darting about everywhere in the body. A person with strong logical thinking ability relies on powerful meditative concentration to achieve single-pointedness, like an awl driven deeply into one point. A person without the power of concentration is like a wooden board laid flat on the ground, leaving no trace.

If your power of concentration is sufficient and your right views are also sufficient, you should combine this with the stillness-based concentration of sitting meditation to strengthen your concentration, and then engage in contemplative practice (vipaśyanā-caryā) of the Buddha's teachings, contemplating the five aggregates (pañcaskandha). Afterwards, investigate Chan, keeping a questioning doubt of investigation constantly in mind. First eliminate self-view (ātma-dṛṣṭi), then investigate Chan to see one's true mind.

The purpose of studying the Dharma is precisely to engage in contemplative practice, and then to realize it. If you cannot engage in contemplative practice, it shows that your power of thinking is not good enough—that is, your power of concentration is not good enough. Meditative concentration without contemplative cultivation cannot play much of a role in realizing the Dharma. Therefore, you should learn to cultivate concentration, so that meditative concentration can fulfill its proper function.