Matthew 5 WEBSTER

Christ had lately called his disciples, and told them that they should be fishers of men; here he tells them further what he designed them to be - the salt of the earth, and lights of the world, that they might be indeed what it was expected they should be.
I. Ye are the salt of the earth. This would encourage and support them under their sufferings, that, though they should be treated with contempt, yet they should really be blessings to the world, and the more so for their suffering thus. The prophets, who went before them, were the salt of the land of Canaan; but the apostles were the salt of the whole earth, for they must go into all the world to preach the gospel. It was a discouragement to them that they were so few and so weak. What could they do in so large a province as the whole earth? Nothing, if they were to work by force of arms and dint of sword; but, being to work silent as salt, one handful of that salt would diffuse its savour far and wide; would go a great way, and work insensibly and irresistibly as leaven, Mat 13:33. The doctrine of the gospel is as salt; it is penetrating, quick, and powerful (Heb 4:12); it reaches the heart Act 2:37. It is cleansing, it is relishing, and preserves from putrefaction. We read of the savour of the knowledge of Christ (Co2 2:14); for all other learning is insipid without that. An everlasting covenant is called a covenant of salt (Num 18:19); and the gospel is an everlasting gospel. Salt was required in all the sacrifices (Lev 2:13), in Ezekiel's mystical temple, Eze 43:24. Now Christ's disciples having themselves learned the doctrine of the gospel, and being employed to teach it to others, were as salt. Note, Christians, and especially ministers, are the salt of the earth.
1. If they be as they should be they are as good salt, white, and small, and broken into many grains, but very useful and necessary. Pliny says, Sine sale, vita humana non potest degere - Without salt human life cannot be sustained. See in this, (1.) What they are to be in themselves - seasoned with the gospel, with the salt of grace; thoughts and affections, words and actions, all seasoned with grace, Col 4:6. Have salt in yourselves, else you cannot diffuse it among others, Mar 9:50. (2.) What they are to be to others; they must not only be good but do good, must insinuate themselves into the minds of the people, not to serve any secular interest of their own, but that they might transform them into the taste and relish of the gospel. (3.) What great blessings they are to the world. Mankind, lying in ignorance and wickedness, were a vast heap of unsavoury stuff, ready to putrefy; but Christ sent forth his disciples, by their lives and doctrines, to season it with knowledge and grace, and so to render it acceptable to God, to the angels, and to all that relish divine things. (4.) How they must expect to be disposed of. They must not be laid on a heap, must not continue always together at Jerusalem, but must be scattered as salt upon the meat, here a grain and there a grain; as the Levites were dispersed in Israel, that, wherever they live, they may communicate their savour. Some have observed, that whereas it is foolishly called an ill omen to have the salt fall towards us, it is really an ill omen to have the salt fall from us.
2. If they be not, they are as salt that has lost its savour. If you, who should season others, are yourselves unsavoury, void of spiritual life, relish, and vigour; if a Christian be so, especially if a minister be so, his condition is very sad; for, (1.) He is irrecoverable: Wherewith shall it be salted? Salt is a remedy for unsavoury meat, but there is no remedy for unsavoury salt. Christianity will give a man a relish; but if a man can take up and continue the profession of it, and yet remain flat and foolish, and graceless and insipid, no other doctrine, no other means, can be applied, to make him savoury. If Christianity do not do it, nothing will. (2.) He is unprofitable: It is thenceforth good for nothing; what use can it be put to, in which it will not do more hurt than good? As a man without reason, so is a Christian without grace. A wicked man is the worst of creatures; a wicked Christian is the worst of men; and a wicked minister is the worst of Christians. (3.) He is doomed to ruin and rejection; He shall be cast out - expelled the church and the communion of the faithful, to which he is a blot and a burden; and he shall be trodden under foot of men. Let God be glorified in the shame and rejection of those by whom he has been reproached, and who have made themselves fit for nothing but to be trampled upon.
II. Ye are the light of the world, Mat 5:14. This also bespeaks them useful, as the former (Sole et sale nihil utilius - Nothing more useful than the sun and salt), but more glorious. All Christians are light in the Lord (Eph 5:8), and must shine as lights (Phi 2:15), but ministers in a special manner. Christ call himself the Light of the world (Joh 8:12), and they are workers together with him, and have some of his honour put upon them. Truly the light is sweet, it is welcome; the light of the first day of the world was so, when it shone out of darkness; so is the morning light of every day; so is the gospel, and those that spread it, to all sensible people. The world sat in darkness, Christ raised up his disciples to shine in it; and, that they may do so, from him they borrow and derive their light.
This similitude is here explained in two things:
1. As the lights of the world, they are illustrious and conspicuous, and have many eyes upon them. A city that is set on a hill cannot be hid. The disciples of Christ, especially those who are forward and zealous in his service, become remarkable, and are taken notice of as beacons. They are for signs (Isa 7:18), men wondered at (Zac 3:8); all their neighbours have any eye upon them. Some admire them, commend them, rejoice in them, and study to imitate them; others envy them, hate them, censure them, and study to blast them. They are concerned therefore to walk circumspectly, because of their observers; they are as spectacles to the world, and must take heed of every thing that looks ill, because they are so much looked at. The disciples of Christ were obscure men before he called them, but the character he put upon them dignified them, and as preachers of the gospel they made a figure; and though they were reproached for it by some, they were respected for it by others, advanced to thrones, and made judges (Luk 22:30); for Christ will honour those that honour him.
2. As the lights of the world, they are intended to illuminate and give light to others (Mat 5:15), and therefore, (1.) They shall be set up as lights. Christ has lighted these candles, they shall not be put under a bushel, not confined always, as they are now, to the cities of Galilee, or the lost sheep of the house of Israel, but they shall be sent into all the world. The churches are the candlesticks, the golden candlesticks, in which these lights are placed, that they light may be diffused; and the gospel is so strong a light, and carries with it so much of its own evidence, that, like a city on a hill, it cannot be hid, it cannot but appear to be from God, to all those who do not wilfully shut their eyes against it. It will give light to all that are in the house, to all that will draw near to it, and come where it is. Those to whom it does not give light, must thank themselves; they will not be in the house with it; will not make a diligent and impartial enquiry into it, but are prejudiced against it. (2.) They must shine as lights, [1.] By their good preaching. The knowledge they have, they must communicate for the good of others; not put it under a bushel, but spread it. The talent must not be buried in a napkin, but traded with. The disciples of Christ must not muffle themselves up in privacy and obscurity, under pretence of contemplation, modesty, or self-preservation, but, as they have received the gift, must minister the same, Luk 12:3. [2.] By their good living. They must be burning and shining lights (Joh 5:35); must evidence, in their whole conversation, that they are indeed followers of Christ, Jam 3:13. They must be to others for instruction, direction, quickening, and comfort, Job 29:11.
See here, First, How our light must shine - by doing such good works as men may see, and may approve of; such works as are of good report among them that are without, and as will therefore give them cause to think well of Christianity. We must do good works that may be seen to the edification of others, but not that they may be seen to our own ostentation; we are bid to pray in secret, and what lies between God and our souls, must be kept to ourselves; but that which is of itself open and obvious to the sight of men, we must study to make congruous to our profession, and praiseworthy, Phi 4:8. Those about us must not only hear our good words, but see our good works; that they may be convinced that religion is more than a bare name, and that we do not only make a profession of it, but abide under the power of it.
Secondly, For what end our light must shine - "That those who see your good works may be brought, not to glorify you (which was the things the Pharisees aimed at, and it spoiled all their performances), but to glorify your Father which is in heaven." Note, The glory of God is the great thing we must aim at in every thing we do in religion, Pe1 4:11. In this centre the lines of all our actions must meet. We must not only endeavor to glorify God ourselves, but we must do all we can to bring others to glorify him. The sight of our good works will do this, by furnishing them, 1. With matter for praise. "Let them see your good works, that they may see the power of God's grace in you, and may thank him for it, and give him the glory of it, who has given such power unto men." 2. With motives of piety. "Let them see your good works, that they may be convinced of the truth and excellency of the Christian religion, may be provoked by a holy emulation to imitate your good works, and so may glorify God." Note, The holy, regular, and exemplary conversation of the saints, may do much towards the conversion of sinners; those who are unacquainted with religion, may hereby be brought to know what it is. Examples teach. And those who are prejudiced against it, may hereby by brought in love with it, and thus there is a winning virtue in a godly conversation.