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:

Wesley's Notes

48:18 As the waves - Infinite and continual.

Jamieson-Fausset-Brown Bible Commentary

18. peace-(Ps 119:165). Compare the desire expressed by the same Messiah (Mt 23:37; Lu 19:42).

river-(Isa 33:21; 41:18), a river flowing from God's throne is the symbol of free, abundant, and ever flowing blessings from Him (Eze 47:1; Zec 14:8; Re 22:1).

righteousness-religious prosperity; the parent of "peace" or national prosperity; therefore "peace" corresponds to "righteousness" in the parallelism (Isa 32:17).

Matthew Henry's Concise Commentary

48:16-22 The Holy Spirit qualifies for service; and those may speak boldly, whom God and his Spirit send. This is to be applied to Christ. He was sent, and he had the Spirit without measure. Whom God redeems, he teaches; he teaches to profit by affliction, and then makes them partakers of his holiness. Also, by his grace he leads them in the way of duty; and by his providence he leads in the way of deliverance. God did not afflict them willingly. If their sins had not turned them away, their peace should have been always flowing and abundant. Spiritual enjoyments are ever joined with holiness of life and regard to God's will. It will make the misery of the disobedient the more painful, to think how happy they might have been. And here is assurance given of salvation out of captivity. Those whom God designs to bring home to himself, he will take care of, that they want not for their journey. This is applicable to the grace laid up for us in Jesus Christ, from whom all good flows to us, as the water to Israel out of the rock, for that Rock was Christ. The spiritual blessings of redemption, and the rescue of the church from antichristian tyranny, are here pointed to. But whatever changes take place, the Lord warned impenitent sinners that no good would come to them; that inward anguish and outward trouble, which spring from guilt and from the Divine wrath, must be their portion for ever.