Isaiah 48:18

“O that thou hadst hearkened to my commandments! then had thy peace been as a river, and thy righteousness as the waves of the sea:”

Wilhelmus a Brakel (1635-1711)

When God is said to desire something which does not occur, such as when He states, “O that there were such a heart in them, that they would fear Me,...that it might be well with them, and with their children for ever!” (Deu. 5:29), or, “O that thou hadst hearkened to My commandments! then had thy peace been as a river” (Isa. 48:18), He is speaking in the manner of men. Strictly speaking, such can never be said concerning the omniscient, omnipotent, immutable, and most perfect God. Rather, it indicates God’s displeasure toward sin and how He delights in holiness. It indicates that sin is the reason why those blessings are withheld from them – blessings which they, according to His promise, would have received as a reward upon godliness. The promises are made upon condition of obedience which is granted to the elect according to God’s immutable purpose. When God says, “Have I any pleasure at all that the wicked should die? saith the Lord God: and not that He should return from His ways, and live?” (Ezek. 18:23), this does not suggest that God’s will is impotent. Rather, it indicates that God has no pleasure in the destruction of men, inasmuch as they are His creatures. He has pleasure in the exercise of righteousness and godliness, and in blessing the godly.

(From: “The Christian’s Reasonable Service”)

Matthew Poole (1624-1679)

O that thou hadst hearkened to my commandments! the failure hath not been on my part, but on thine: I gave thee my counsels and commands, but thou hast neglected and disobeyed them, and that to thy own great disadvantage. Such wishes as these are not to be taken properly, as if God longed for something which he gladly would but could not effect, or as if he wished that to be undone which was irrevocably past and done; which is a vain and foolish wish even in a man; and much more are such wishes inconsistent with the infinite perfection and happiness of the Divine nature; but they are only significations of God’s good and holy will, whereby he requires and loves obedience, and condemns and hates disobedience.

(From: “A Commentary on the Holy Bible”)