It is his own heart that the person wants to be pure. The heart is a synecdoche for the person. AT: "loves having a pure heart" or "wants to be pure" (See: [[rc://en/ta/man/translate/figs-synecdoche]])
The eyes are a synecdoche for the person. The writer speaks as if Yahweh had physical eyes like a person. AT: "Yahweh keeps watch over" or "Yahweh guards knowledge" (See: [[rc://en/ta/man/translate/figs-synecdoche]] and [[rc://en/ta/man/translate/figs-personification]])
The nominal adjective treacherous can be translated as a noun phrase. Translate "treacherous" as in [Proverbs 11:3](../11/03.md). AT: "a treacherous person" (See: [[rc://en/ta/man/translate/figs-nominaladj]])