Isaiah 1:21

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

The verse sets a faithful city that was once full of justice with righteousness dwelling in it against its present state as unfaithful like a prostitute, corrupt and violent with murderers where righteousness had lived. The change is from former faithfulness to present violence and injustice, with murder taking the place of faithfulness. Jerusalem is pictured as having once upheld justice and righteousness and then turning from that faithfulness.

It describes Israel and Jerusalem in the days of Christ as fulfilling this picture. Its silver had become dross and its wine mixed with water, and its princes were rebellious and companions of thieves, loving gifts and following after rewards while neglecting the fatherless and the widow. Even then Christ still pleaded with the rebellious and wept over the beloved city, while the Lord declared He would relieve Himself of His adversaries and take vengeance on His enemies.

The faithful city becomes unfaithful when people who have had every opportunity to know the truth become defiled by the corruptions of the ungodly. It pictures those who, after testing and long connection with those laboring for them, show no purification from wrong habits and practices, act dishonestly and without straightforwardness in temporal or spiritual dealings, and treat great mercies as common. It means mingling the sacred with the common while professing to believe the truth, trying to carry dishonest practices through the narrow way, and choosing by action the road the world travels. The same image applies to a church that claims righteousness while concealing a defiled character and hiding moral corruption beneath a show of righteousness. Such corruption drives away the divine presence and glory and leaves the community weak and without strength.

The indictment of murder in place of faithfulness applies to liquor dealers and those who enable the liquor trade, whose actions help lead people to violence and murder and leave them answerable for the resulting bloodshed. The verse is a warning to turn from sinful conduct, to cease doing evil and learn to do well while divine mercy is still available.