Charles Ellicott Commentary Matthew 27:65

"Pilate said unto them, Ye have a guard: go, make it [as] sure as ye can." — Matthew 27:65 (ASV)

You have a watch —Better, Take a guard. The Greek verb may be either imperative or indicative. The former gives the better meaning. The “watch,” or “guard,” was a body of Roman soldiers (St. Matthew uses the Latin term custodia), who could not be set to such a task without Pilate’s permission. If the priests had had such a “guard” at their disposal before, there would have been no need for them to apply to Pilate.