Two things that pertain to the office of a teacher (Thomas Aquinas)

[Reformed Covenanter]

There are two things that pertain to the office of a teacher: to instruct the devout or sincere, and to repel opponents.

Thomas Aquinas, Super Evangelium S. Ioannis Lectura (1270-72), C8.L1.n1118.9.

N.B. This comment sounds very similar to a famous John Calvin quote.