Behold, the Lord's hand is not shortened— The prophet here teaches, that the reason why God does not exert his power for the avenging of his people, is not because his hand is shortened, but because he doth not hear their prayers; that he does not hear, not because his ear is grown heavy, but because an intermediate cloud, namely, of their sins, hinders his face from being seen by them in favour, or their prayers from being heard or regarded by him: as much as to say, "The reason of the continuance of your calamities is not want either of power in God to deliver you, or of goodness to hear your prayers; but your iniquities render him a stranger to you, and stop the course of his blessings." See Vitringa.
Related Commentaries of Isaiah 59:1
Isaiah 59:1-2
1 Behold, the LORD'S hand is not shortened, that it cannot save; neither his ear heavy, that it cannot hear:
2 But your iniquities have separated between you and your God, and your sins have hida his face from you, that he will not hear.