Them that sin rebuke before all, that others also may fear.
Them that sin - habitually (present participle), whether presbyters or laymen.
Rebuke before all - by ecclesiastical authority, publicly before the church, it being a case not of mere individual offence, but a public scandal (Matthew 18:15-17; 1 Corinthians 5:9-13; Ephesians 5:11). Not until this "rebuke" was disregarded was the offender excommunicated.
That others also may fear - offending (Deuteronomy 13:11; Acts 5:11).