As if He says, “If a man who has once been enlightened by the seasoning of truth, falls back into apostacy, by what other teacher shall he be corrected, seeing that the sweetness of wisdom which he tasted he has cast away, alarmed by the troubles or allured by the attractions of the world; hence it follows, It is neither fit for the land, nor yet for the dunghill, &c. For salt when it has ceased to be fit for seasoning food and drying flesh, will be good for nothing. For neither is it useful to the land, which when it is east thereon is hindered from bearing, nor for the dunghill to benefit the dressing of the land. So he who after knowledge of the truth falls back, is neither able to bring forth the fruit of good works himself, nor to instruct others; but he must be cast out of doors, that is, must be separated from the unity of the Church.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).