Jamieson, Fausset and Brown on Isaiah 49:9

9. (Is 42:7; Zec 9:12).

prisoners--the Jews bound in legal bondage.

them ... in darkness--the Gentiles having no light as to the one true God [Vitringa].

Show yourselves--not only see but be seen (Mt 5:16; Mr 5:19). Come forth from the darkness of your prison into the light of the Sun of righteousness.

in the ways, &c.--In a desert there are no "ways," nor "high places," with "pastures"; thus the sense is: "They shall have their pastures, not in deserts, but in cultivated and inhabited places." Laying aside the figure, the churches of Christ at the first shall be gathered, not in obscure and unknown regions, but in the most populous parts of the Roman empire, Antioch, Alexandria, Rome, &c. [Vitringa]. Another sense probably is the right one. Israel, on its way back to the Holy Land, shall not have to turn aside to devious paths in search of necessaries, but shall find them in all places wherever their route lies; so Rosenmuller. God will supply them as if He should make the grass grow in the trodden ways and on the barren high places.