Shared ground
These verses give the stated reason for the harsh curse language earlier in the psalm: the enemy showed a settled pattern of cruelty. He “didn’t remember” kindness and instead hunted down the poor, needy, and brokenhearted “to kill” (v.16). The complaint is not just about personal insult; it includes violence against vulnerable people and destructive speech against the speaker’s life (v.20).
The passage also uses a “what you chose comes back on you” logic. Because the enemy loved cursing and rejected blessing, the poem pictures curse as something that returns to him and sticks to him like clothing and a belt, even sinking inward like water and oil (vv.17–19). Verse 20 closes by framing this as Yahweh’s “reward” (payback) for the speaker’s adversaries—especially those who speak evil against him.
Where interpretation differs (only where needed)
Some read “he” as one particular opponent in the speaker’s real-life case; others take him as a representative kind of person—an archetype of the ruthless slanderer and oppressor. Both readings fit the way the psalm moves between a specific dispute and broad moral language.
Some take “to kill them” (v.16) and the imagery of curse entering the body (v.18) as close to literal intent and outcome; others hear it mainly as poetic intensification—language designed to show the depth of harm and the completeness of reversal.
Some read v.20 (“reward … from Yahweh”) as describing direct divine action in judgment; others understand it as God allowing the person’s chosen pattern to recoil on him—still “from Yahweh” in the sense that God governs moral outcomes.
Why the disagreement exists
The passage mixes courtroom-like claims (false speech against the speaker, v.20) with vivid poetry (curse as clothing and oil, vv.18–19). Because poetry often speaks in images rather than report-style detail, readers differ on how far to press the language into specifics. Also, the psalm never names the enemy, leaving “he” open as either a single figure or a portrait.
What this passage clearly contributes
Explicitly, it ties the requested curses to a moral rationale: persistent harm to the vulnerable and persistent love of cursing. It also presents a strong principle of fitting consequence: what a person embraces—cursing instead of blessing—becomes what surrounds him and shapes his life (vv.17–19). Finally, it connects the outcome to Yahweh’s just response to those who attack and slander the speaker’s life (v.20), not merely to the speaker’s private desire for revenge.