Isaiah 1:21

How is the faithful city become an harlot! it was full of judgment; righteousness lodged in it; but now murderers.

How is the faithful city become a harlot!.... The city of Jerusalem, in which were the temple, and the pure worship of God, and was in the tribe of Judah, which ruled with God, and was very faithful with the saints when the ten tribes revolted, and fell in with the sin of Jeroboam; but now, in Isaiah's time, was become like a treacherous wife to her husband, unfaithful to the Lord, went after other lovers, committed spiritual adultery, that is, idolatry, with stocks and stones; and in the times of Christ were a wicked and an adulterous generation, corrupting the word and worship of God; see Matthew 12:39

it was full of judgment; strict justice was exercised privately between man and man, as well as in the public courts of judicature;

righteousness lodged in it; that is, righteous men, who walked in all the commandments of the Lord, and lived soberly, righteously, and godly; see 2 Peter 3:13

but now murderers: of the prophets whom they stoned, who were sent unto them, and of the Lord Jesus Christ, of whom they were the betrayers and murderers; see Matthew 23:37.