Is waxed gross (επαχυνθη). Aorist passive tense. From παχυς, thick, fat, stout. Made callous or dull -- even fatty degeneration of the heart.

Dull of hearing (τοις ωσιν βαρεως ηκουσαν). Another aorist. Literally, "They heard (or hear) heavily with their ears." The hard of hearing are usually sensitive.

Their eyes they have closed (τους οφθαλμους αυτων εκαμμυσαν). The epic and vernacular verb καμμυω is from καταμυω (to shut down). We say shut up of the mouth, but the eyes really shut down. The Hebrew verb in Isaiah 6:10 means to smear over. The eyes can be smeared with wax or cataract and thus closed. "Sealing up the eyes was an oriental punishment" (Vincent). See Isaiah 29:10; Isaiah 44:18.

Lest (μηποτε). This negative purpose as a judgment is left in the quotation from Isaiah. It is a solemn thought for all who read or hear the word of God.

And I should heal them (κα ιασομα αυτους). Here the LXX changes to the future indicative rather than the aorist subjunctive as before.