How to Make the Thinking of Mind Consciousness Deep, Subtle, and Clear?

Under what circumstances can the thinking function of the mind consciousness be exercised to the greatest extent, so that deliberation (manasikāra) is at its best and clearest? When the mind consciousness attends to only one dharma, or takes one dharma as the main object while attending to two or three dharmas, moving from distraction toward focus, deliberation is at its clearest—this is the function of meditative concentration (samādhi). When the mind is distracted, the mind consciousness's power of deliberation is weak and the train of thought is unclear. When concentration is too deep, the mind consciousness cannot move, mental activity ceases, and deliberation becomes very laborious. Only when there is concentration, and the concentration is not excessively deep, can the mind consciousness's deliberation be deep, subtle, and clear, with an open and expansive train of thought.