Luke 14:35

He had said above that the tower of virtue was not only to be begun, but also to be completed, and to this belongs the following, Salt is good. It is a good thing to season the secrets of the heart with the salt of spiritual wisdom, nay with the Apostles to become the salt of the earth. (Matt. 5:14.) For salt in substance consists of water and air, having a slight mixture of earth, but it dries up the fluent nature of corrupt bodies so as to preserve them from decay. Fitly then He compares His disciples to salt, inasmuch as they are regenerated by water and the Spirit; and as living altogether spiritually and not according to the flesh, they after the manner of salt change the corrupt life of men who live on the earth, and by their own virtuous lives delight and season their followers. 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. Let him hear also not by despising, but by doing what he has learnt.

But not only those who are gifted with the grace of teachers, but private individuals also He requires to become like salt, useful to those around them. But if he who is to be useful to others becomes reprobate, he cannot be profited, as it follows, But if the salt has lost his savour, where-with shall it be seasoned? But because His discourse was in parables and dark sayings, our Lord, in order to rouse His hearers that they might not receive indifferently what was said of the salt, adds, He that hath ears to hear, let him hear, that is, as he has wisdom let him understand. For we must take the ears here as the perceptive power of the mind and capacity of understanding.