Albert Barnes Commentary Proverbs 17:15

"He that justifieth the wicked, and he that condemneth the righteous, Both of them alike are an abomination to Jehovah." — Proverbs 17:15 (ASV)

People need to be warned against an unjust acquittal, no less than against unjust condemnation. The word “justifieth” has its forensic sense, “to declare righteous,” to acquit.