Benefit of clergyIn medieval England, the benefit of clergy, begun about the 12th century, meant that those to whom the term applied could not be tried or legally punished by the secular legal system. If they were accused of crimes, they were tried under canon law. One penalty possible under canon law was defrocking, and a defrocked priest could be subjected to further penalty under the secular laws. The issue of the "criminous clerks," clergymen accused of crime, was long a subject of great dispute in England, and was at the heart of the quarrel between Henry II and St. Thomas Becket.
In England especially, the definition of clergy was extended to include all who could read and write; see Ben Jonson.
The benefit of clergy had to be pled by a certain ritual, after conviction and before sentencing. The accused then had to read aloud a verse from the Bible; by tradition, the passage chosen was inevitably and appropriately Psalm 51, Miserere mei, Domine. (Have mercy upon me, O God.)1 As a result, this Psalm became known as the "neck verse;" knowing it could save your neck. Clergy could be pled but once; those who were convicted of a second felony were ineligible. Many crimes came to be defined by Parliament as "unclergyable;" in the words of the statutes, they were "felony without benefit of clergy."
1Psalm 50 according to the Vulgate numbering.