Jamieson, Fausset and Brown on Isaiah 42:19

19. my servant--namely, Israel. Who of the heathen is so blind? Considering Israel's high privileges, the heathen's blindness was as nothing compared with that of Israelite idolaters.

my messenger ... sent--Israel was designed by God to be the herald of His truth to other nations.

perfect--furnished with institutions, civil and religious, suited to their perfect well-being. Compare the title, "Jeshurun," the perfect one, applied to Israel (compare Is 44:2), as the type of Messiah [Vitringa]. Or translate, the friend of God, which Israel was by virtue of descent from Abraham, who was so called (Is 41:8), [Gesenius]. The language, "my servant" (compare Is 42:1), "messenger" (Mal 3:1), "perfect" (Ro 10:4; He 2:10; 1Pe 2:22), can, in the full antitypical sense, only apply to Christ. So Is 42:21 plainly refers to Him. "Blind" and "deaf" in His case refer to His endurance of suffering and reproach, as though He neither saw nor heard (Psa 38:13, 14). Thus there is a transition by contrast from the moral blindness of Israel (Is 42:18) to the patient blindness and deafness of Messiah [Horsley].