Jamieson, Fausset and Brown on Isaiah 49:8

8. Messiah is represented as having asked for the grace of God in behalf of sinners; this verse contains God the Father's favorable answer.

an acceptable time--"In a time of grace" [Hengstenberg]. A limited time (Is 61:2; 2Co 6:2). The time judged by God to be the best fitted for effecting the purposes of His grace by Messiah.

heard thee--(Psa 2:8; He 5:7).

day of salvation--when "the fulness of time" (Ga 4:4) shall have come. The day of salvation is "to-day" (He 4:7).

helped--given Thee the help needed to enable Thee, as man, to accomplish man's salvation.

preserve--from the assaults and efforts of Satan, to divert Thee from Thy voluntary death to save man.

covenant of the people--(See on Is 42:6). "The people," in the singular, is always applied exclusively to Israel.

establish the earth--rather, "to restore the land," namely, Canaan to Israel. Spiritually, the restoration of the Church (the spiritual Israel) to the heavenly land forfeited by man's sin is also included.

cause to inherit ... desolate heritages--image from the desolate state of Judea during the Babylonish captivity. Spiritually, the Gentile world, a moral waste, shall become a garden of the Lord. Literally, Judea lying desolate for ages shall be possessed again by Israel (compare Is 61:7, "in their land"). Jesus, the antitype of, and bearing the same name as Joshua (He 4:8), shall, like him, divide the land among its true heirs (Is 54:3; 61:4).