What is Legis Minister Non Tenetur, In Executione Officii Sui, Fugere Aut Retrocedere?

Legal Definition
The minister of the law is bound, in the execution of his office, not to fly nor to retreat Branch, Prine,
-- Black's Law Dictionary
Legal Definition
A servant of the law is not bound, in the execution of his office, either to flee or to retreat.
-- Ballentine's Law Dictionary