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.
This is a conditional promise: if you obey the commandments, then you will have peace like a river and righteousness like the waves. The implication of this warning, of course, is that you did not keep the Commandments of God; therefore, you are missing out on peace and righteousness. Because you are sinners, you cannot find peace and you do not have righteousness. The Lord wishes His people had kept the commandments for then they would have peace and righteousness. That would be good for them and God would be pleased.
But we did not obey; therefore, the promises cannot be fulfilled and we will never enjoy peace and righteousness. However, one man did hearken to God’s commandments. That man is enjoying peace like a river and righteousness like the waves. God is pleased with that man.
The only hope for all the rest of mankind is to identify with The Man, Christ Jesus, by faith. If you believe in Jesus you, with Him, have kept the Law perfectly; therefore, you have peace like a river. “Since we have been justified by faith we have peace with God through our Lord Jesus Christ.” And, since we are justified by faith we have righteousness like the waves of the sea.
By faith we may claim peace like a river. Jesus gives it to us. When our sins are forgiven we have peace with God for sins no longer separate us from Him; we have inward peace for our sins no longer accuse us and produce guilt; we have peace with others for we forgive them their trespasses as God has forgiven ours.
Our faith is counted to us for righteousness, as the waves of the sea. The waves of the righteousness of God wash over us, cleanse us, refresh us, and drive us forward. Repentance and faith gives us peace and calm every time we hear the Gospel. The world cannot give that kind of peace