Thomas Aquinas Commentary Matthew 5:13

"Ye are the salt of the earth: but if the salt have lost its savor, wherewith shall it be salted? it is thenceforth good for nothing, but to be cast out and trodden under foot of men." — Matthew 5:13 (ASV)

You are the salt of the earth. The Lord showed the Apostles’ dignity in that in tribulations they ought not only to be patient but joyful; now, however, He speaks of their excellence in that they ought to restrain others from evil, and therefore He compares them to salt: You are the salt of the earth. And about this He does two things: firstly, He describes their duty of keeping others from evil; and secondly, He shows how they ought to keep themselves from evil, where it is said: But if the salt lose its savour.

He says, therefore: You are the salt. He compares them to salt for four reasons.

The first reason is because of the production of salt, which comes from both the wind and the sun’s heat: for spiritual generation is from the water of Baptism and the power of the Holy Ghost; Unless a man be born again of water and the Holy Ghost, he cannot enter into the kingdom of God (John 3:5). The production of salt also comes from the heat of the sun, meaning from the fervor of love which is from the Holy Ghost; The charity of God is poured forth in our hearts, by the Holy Ghost who is given to us (Romans 5:5).

Secondly, He compares them to salt because of its usefulness. Its first use is that all things are seasoned with salt; hence, it signifies the wisdom that apostolic men ought to have: The wisdom of doctrine is according to her name, and she is not manifest unto many, but with them to whom she is known, she continueth even to the sight of God , and, Walk with wisdom towards them that are without, redeeming the time (Colossians 4:5). Its second use was that in every sacrifice salt was added (Leviticus 2:13), because apostolic teaching ought to be reflected in our every deed. Its third use is that it absorbs excess moisture and by this preserves from putrefaction. In this way the Apostles were restraining carnal concupiscences by their teaching: The time past is sufficient to have fulfilled the will of the Gentiles, for them who have walked in riotousness, lusts, excess of wine, revellings, banquetings and unlawful worshipping of idols (1 Peter 4:3), and, Let us walk honestly, as in the day: not in rioting and drunkenness, not in chambering and impurities, not in contention and envy (Romans 13:13).

The fourth effect of salt is that it makes the ground sterile. Hence, it is said that some conquerors sowed salt extensively outside a city they captured so that nothing would grow. In the same way, the Gospel teaching also makes the ground sterile, that is, so that earthly works do not spring up in us; And have no fellowship with the unfruitful works of darkness: but rather reprove them (Ephesians 5:11).

Therefore, the Apostles are called salt because they possess a pungency that turns people away from sins; Have salt in you: and have peace among you (Mark 9:49).

But someone might say, ‘It is enough that I have salt.’ On the contrary, it is necessary that the power of salt keep you from sin, and for this He cites four reasons:

1. The first is taken from its incorrigibility. Hence it is said, But if the salt lose its savor, wherewith shall it be salted? Those things properly lose their savor that lose their strength: just as strong wine sometimes loses its strength, so salt sometimes loses its pungency; But if the salt become unsavoury, wherewith will you season it? (Mark 9:49). Hence, one then loses his savor when he is guilty of sin; They became vain in their thoughts. And their foolish heart was darkened (Romans 1:21). If, therefore, because of tribulations or some other reason you withdraw from virtue, with what will you be salted? Meaning, with what other thing will you be salted with salt? For if the people sin they can be corrected, but if a prelate sins, no one can reform him; How long will they be incapable of being cleansed? (Hosea 8:5). And it ought to be observed that in Luke 14:34, it is said: But if the salt shall become tasteless (infatuatum). For it is great foolishness (fatuitas) to relinquish eternal things for temporal things.
2. The second reason is its uselessness if it loses its savor; hence, it is said: It is good for nothing. He explains this in Luke 14:35, where it is said: Neither profitable for the land nor for the dunghill, because it makes the land sterile and does not fertilize it. So spiritual men, when they sin, can do nothing, because they cannot do secular business as soldiers or similar men can; Son of man, what shall be made of the wood of the vine…? Shall wood be taken of it, to do any work, or shall a pin be made of it for any vessel to hang thereon? Behold it is cast into the fire for fuel… shall it be useful for any work? (Ezekiel 15:2–4), and, They are all gone aside, they are become unprofitable together (Psalms 13:3).
3. The third reason is taken from the imminent danger, which has two aspects corresponding to two dangers. The first is expulsion; hence: but to be cast out, namely, from the Church. Without are dogs and sorcerers and unchaste and murderers and servers of idols and every one that loveth and maketh a lie (Revelation 22:15). Likewise, the dignity of priestly teaching is taken away from him: Because thou hast rejected knowledge, I will reject thee, that thou shalt not do the office of priesthood to me (Hosea 4:6), and, Therefore I say to you that the kingdom of God shall be taken from you and shall be given to a nation yielding the fruits thereof (Matthew 21:43). And so it is said, but to be cast out. The second danger is being made worthless, because those who first live supernaturally and then fail become contemptible. And so it is said: and to be trodden on by men. This man began to build and was not able to finish (Luke 14:30), and, You have departed out of the way, and have caused many to stumble at the law: you have made void the covenant of Levi, saith the Lord of hosts. Therefore have I also made you contemptible, and base before all people, as you have not kept my ways (Malachi 2:8–9). And it ought to be observed, according to Augustine, that if some holy men are made worthless, as it is said above, And they shall speak all that is evil against you, untruly, for my sake (Matthew 5:11), still they can never be trodden on, because they always have their hearts in heaven, and those who lie on the earth are properly trodden on.

You are the light of the world. Here the third dignity of the Apostles is presented. For, just as they ought to keep others away from evils, so they also ought to enlighten them. And concerning this He does two things: firstly, He shows their dignity, and secondly, He counters their timidity, where it is said, A city seated on a mountain cannot be hid.

He says, therefore: You are the light of the world, meaning that they are not only the light of Judea or of Galilee, but also of the whole world; For so the Lord hath commanded us: I have set thee to be the light of the Gentiles: that thou mayest be for salvation unto the utmost part of the earth (Acts 13:47). And this was marvelous, that their light was hardly known in their own land and yet it went out into the whole world. But it is objected that this word He uses, light, seems to apply only to Christ; [John the Baptist] was not the light, but was to give testimony of the light, and afterwards it is said that [Christ] was the true light (John 1:8–9). I answer that only Christ is the light essentially, but the Apostles are called illuminated lights, that is, by participation, just as the eye is an illuminating light and yet it is illuminated.

And observe that these three things, namely: Blessed are ye when they shall revile you, You are the salt of the earth, and You are the light of the world, seem to pertain to the three last beatitudes: namely, the first to Blessed are they that suffer persecution for justice’ sake, the second to Blessed are the peacemakers, meaning they pacify themselves and others, and the third to Blessed are the clean of heart. For if the Apostles were outstanding in these three beatitudes, all the more were they outstanding in the previous beatitudes.

The Lord had said, Blessed are ye when they shall revile you, and, Blessed are they that suffer persecution for justice’ sake; therefore, they might say, ‘If we ourselves will endure so many persecutions, then we want to hide ourselves.’ And for that reason the Lord afterwards counters their timidity, and hence it is said, A city seated on a mountain cannot be hid. And firstly, He forbids their hiding, and secondly, He shows how they ought to show themselves, where it is said, So let your light shine before men. He proves that they ought not to hide themselves for two reasons. Firstly, that they could not hide themselves even if they wanted to do so, and this is what is said, A city seated on a mountain cannot be hid; and secondly, that they ought not to hide themselves, and this is what is said: Neither do men light a candle and put it under a bushel.