wise, fast learner
聡 centers on mental sharpness and quick understanding: being wise and able to learn fast. The two given meanings are closely linked, as wisdom often comes from the ability to absorb and process information rapidly.
聡 combines 耳 (ear) with 忩, a component that likely contributes the sound and the idea of mental activity (through 心, heart/mind). The character suggests sharp hearing as a metaphor for quick understanding.
An ear (耳) connected to a heart/mind (心, inside 忩) suggests someone who listens carefully and processes information quickly, becoming wise.
For ソウ, imagine a wise soul (ソウ) whose fast learning comes from deep listening: soul -> ソウ, and the ear (耳) catches every word.