Alcuin of York

The thief cometh not but for to steal, and to kill. As if He said, And well may the sheep not hear the voice of the thief; for he cometh not but for to steal: he usurpeth another’s office, forming his followers not on Christ’s precepts, but on his own. And therefore it follows, and to kill, i. e. by drawing them from the faith; and to destroy, i. e. by their eternal damnation.