Isaiah 1:19

If ye be willing and obedient. Isaiah here sets forth the fruitage of obedience. A life of joy and blessedness is the natural result of obedience to the laws of God, for God cannot bless those who do not do their best. The joys of heaven are not arbitrary gifts of God to those who follow Him, but the natural result of compliance with His requirements. God sets before man the ways of righteousness because they are right and because they bring blessing in their train.

Ye shall eat. This promise applies both to this world and to the world to come. The harvest of obedience is reaped not only in heaven but also on earth (see on Matt. 19:29). Before Israel entered the Promised Land Moses set forth the blessings that would be theirs if they walked in the ways of the Lord (Deut. 28:1-13). Isaiah points out that these blessings had not been realized because of Israel’s failure to obey the commands of the Lord, God now assures them that these blessings may still be theirs if they will repent and walk in the ways of righteousness.