Shared ground
Proverbs 23:9–11 links two areas of life: speech and property. First, it assumes that some people are not merely uninformed but committed to rejecting wise counsel; in that setting, speaking “in the ears of a fool” leads to contempt rather than learning. Second, it treats land theft by stealth—moving long-standing boundary markers or edging into an orphan’s field—as a serious wrong.
A key stated claim is accountability. The “fatherless” are pictured as socially vulnerable, yet not defenseless. A “Defender” is said to be strong and to take up their case against the person who encroaches.
Where interpretation differs (only where needed)
Some readers take “fool” mainly as a person lacking understanding, so the line warns against poorly timed instruction that won’t be heard. Others take “fool” as someone stubbornly resistant to correction, so the line is about the futility of addressing a person who is set on despising wisdom.
For “Defender,” some read the term as God acting as advocate and judge for the vulnerable. Others think it may include a human role (such as a family redeemer or legal protector) while still implying that God stands behind the cause of the fatherless.
Some also read the “ancient boundary stone” strictly literally (real property markers). Others treat it as a concrete example that can stand for broader forms of taking advantage of the vulnerable, without losing its original land-and-inheritance setting.
Why the disagreement exists
The passage uses short, compressed sayings. Words like “fool” and “Defender” can point to more than one real-life referent, and the proverb does not spell out the mechanism (human court action, divine action, or both) by which the case is “pleaded.”
What this passage clearly contributes
Explicitly, it states that (1) certain speech efforts are wasted because the hearer will despise wise words, and (2) boundary-tampering and encroachment on the orphan’s land are forbidden, with (3) a strong Defender who will oppose the encroacher. Theologically inferred from these claims is that wisdom teaching assumes a moral order in which exploitation, especially against the unprotected, meets active resistance and real accountability.