Matthew 5:13

The former instructions Jesus Christ gave to the multitude. Now he addresses his apostles, styling them the salt of the earth, meant to preserve men from the corruption of sin, and to make them relish the truths of salvation. He tells them not to suffer their faith or their charity to slacken, in which all their power consists, lest they come to be rejected by God, and despised by man. (Calmet) --- I send you, says Jesus Christ, not to two, ten, or twenty cities, not to one single nation, as the prophets were sent, but to the whole world, a world oppressed with numberless iniquities. It is not the property of salt to restore what is already corrupted, but to preserve from corruption. Therefore the virtue of the merits of Christ delivers us from the corruption of sin; but the care and labour of the apostles preserves us from again returning to it. (St. John Chrysostom, hom. xv.) --- It appears from Luke xiv. 34, that this comparison is taken from agriculture. We observe these properties of salt in the different manures that fertilize the soil, but suffer the salts to evaporate, and all their virtue is lost. (Haydock)