肇論新疏 2.240

2.240

悟發者，謂遇什公，明悟開發也。淵對，指什公。開究下，謂開解窮究般若之道，想足盡了過半之思。意云：已盡過半，語用〈繫辭〉，謂悟極聖心也。故每下，劉公每思南北乖違疎闊，不親一見，憤愧深也。

"Understanding blooms" means that having encountered Kumārajīva, his clear understanding opened and unfolded. "Profound dialogue partner" refers to Kumārajīva. From "uncovering and investigating" onward: it means uncovering and investigating the path of prajñā to the utmost; he imagines it is sufficient to exhaust more than half of one's thoughts. The meaning is: having already exhausted more than half; the phrasing is taken from the Xici [of the Yijing], meaning that he understands the sage mind to the utmost limit. From "Thus, whenever" onward: Master Liu always reflects that north and south are separated and distant, and he cannot meet him in person, so his distress and shame are deep.