ל֥וּא הִקְשַׁ֖בְתָּ לְמִצְוֺתָ֑י וַיְהִ֤י כַנָּהָר֙ שְׁלוֹמֶ֔ךָ וְצִדְקָתְךָ֖ כְּגַלֵּ֥י הַיָּֽם׃
Oh that thou wouldest hearken to My commandments! Then would thy peace be as a river, And thy righteousness as the waves of the sea;
Read halakhic rulings (Jewish law) on Isaiah 48:18 from the Mishneh Torah and classical halakhic sources, free online.