Mona (“sagacity”, Sanskrit mauna) is the abstract noun from muni (‘sage”). Over time it acquired the sense “silence”, as a thoughtful man is silent, and it is explained as such here by the commentary as well as the Chinese translation (T 210:27.13 at T iv 586c19). However I have not found any early instances to support this. In Pali, silence is tuṇhī; a “vow of silence”—forbidden to monastics—is mūgabbata (Kd 4:1.12.6). Nothing in the context here suggests a vow of silence. In the Rig Veda (7.56.8, 10.136) the muni appears as an ecstatic, raving as if drunk, apparently from drugs (soma, viṣa), suggesting a sense of “mind-altered” or “mind-expanded”. Chāndogya Upaniṣad 8.5.2 refers to mauna as the life of a student, characterized by manute (“thinking”, “reflection”), so we can well translate “thoughtfulness”. Bṛhadāraṇyaka Upaniṣad 3.5.1 enjoins the student to become like a child, then reject both scholarship and childishness, thus becoming a “sage” (muni). Then, rejecting sagacity and lack of sagacity they become a brahmin. This could easily have the Vedic sense of “mind-expanded (through drugs or meditation)”. A similar sense probably applies here. The verse enjoins “weighed” or rational thought as opposed to confused, perhaps “ecstatic” or “mind-altered” thought.

These two lines recapitulate the previous lines. Munāti (“sagely weighs”, literally “thinks, examines”) is punned with mināti (“measure, weigh”) following the imagery of the scales. “Both” calls back to both good and evil.