"Wounding blows cleanse away evil" (20:30). What is this saying about?

The saying has two halves: "Wounding blows cleanse away evil, and beatings purge the innermost parts" (20:30). It names no rod and no child, and it doesn't say who strikes; it speaks of blows and of what they reach. Cleanse away is tamruq, which Strong's gives as "properly, a scouring, i.e. soap or perfumery for the bath; figuratively, a detergent". The Hebrew Bible has it only here and three times in Esther 2, where the WEB gives it as cosmetics (Esther 2:3, 2:9) and preparations for beautifying women (Esther 2:12). The second half has no Hebrew word for purge; the WEB supplies it. The innermost parts are, in Hebrew, the words of 20:27, where the LORD's lamp searches "all his innermost parts" (20:27) (tap innermost parts). The book speaks of the rod in other sayings (Proverbs 13:24, 22:15, 23:13-14, 29:15), and the notes on Proverbs 13 look at 13:24. These notes explain 20:30 only from its own words; they don't apply it to any modern practice, law or debate, or say how anyone should discipline anyone. If this saying touches anyone harmed at home, make room to talk, and help them find someone they trust to talk to further, such as a pastor or a counselor.