clean, pure, cleanse
凈 centers on cleanliness and purity: making something free of dirt or impurity, or being in a clean, pure state.
凈 is a variant form of 淨, combining 冫 (ice) with 爭, which likely contributes the sound. The ice radical suggests purity or cleansing through coldness. The exact historical development is uncertain.
The left side 冫 suggests ice, and the right side 爭 looks like a hand holding a brush. Imagine using an icy brush to scrub something until it is clean and pure.
For ソウ, picture cleaning a surface with a soft, icy cloth: soft -> ソウ, and the ice-cold cloth makes everything pure.