isaiah 6:10 Make the heart of this people fat, and make their ears heavy, and shut their eyes; lest they see with their eyes, and hear with their ears, and understand with their heart, and convert, and be healed. - Free Bible Online

      10. Make . . . fat-- (Ps 119:17). "Render them the more hardened by thy warnings" [MAURER]. This effect is the fruit, not of the truth in itself, but of the corrupt state of their hearts, to which God here judicially gives them over (Isa 63:17). GESENIUS takes the imperatives as futures. "Proclaim truths, the result of which proclamation will be their becoming the more hardened" (Ro 1:28; Eph 4:18); but this does not so well as the former set forth God as designedly giving up sinners to judicial hardening (Ro 11:8; 2Th 2:11). In the first member of the sentence, the order is, the heart, ears, eyes; in the latter, the reverse order, the eyes, ears, heart. It is from the heart that corruption flows into the ears and eyes (Mr 7:21, 22); but through the eyes and ears healing reaches the heart (Ro 10:17), [BENGEL]. (Jer 5:21; Eze 12:2; Zec 7:11; Ac 7:57; 2Ti 4:4). In Mt 13:15, the words are quoted in the indicative, "is waxed gross" (so the Septuagint), not the imperative, "make fat"; God's word as to the future is as certain as if it were already fulfilled. To see with one's eyes will not convince a will that is opposed to the truth (compare Joh 11:45, 46; 12:10, 11). "One must love divine things in order to understand them" [PASCAL].
      be healed--of their spiritual malady, sin (Isa 1:6; Ps 103:3; Jer 17:14).

JFB.