Chapter 5:13-20 The Salt & Light

5:13 Ye are the salt of the earth: but if the salt have lost his savor, wherewith shall it be salted? it is thenceforth good for nothing, but to be cast out, and to be trodden under foot of men.
Ye are the salt of the earth - Our Lord shows here what the preachers of the Gospel, and what all who profess to follow Him, should be; the salt of the earth, to preserve the world from putrefaction.
But if the salt have lost his savor - A Christian, who has lost the life of Christ, and the witness of his Spirit, out of his soul, may be likened to this salt. He may have the sparks and glittering particles of true wisdom, but without its unction or comfort. Only that which is connected with the rock, the soul that is in union with Christ Jesus by the Holy Spirit, can preserve its savor, and be instrumental of good to others. It is thenceforth good for nothing, but to be cast out and to be trodden under foot. Salt is good for nothing, but to make things savory, and preserve from putrefacation; and when it has lost its savor, it is of no use, neither to men nor beasts, as some things are when corrupted; so ministers of the word, when they have dropped the savory doctrines of the Gospel, as their usefulness is gone.

5:14 Ye are the light of the world. A city that is set on an hill cannot be hid.

Christ never contemplated the production of secret Christians.

5:15 Neither do men light a candle, and put it under a bushel, but on a candlestick; and it giveth light unto all that are in the house.

Neither do men light a candle - Which may be read impersonally, "a candle is not lighted".

5:16 Let your light so shine before men, that they may see your good works, and glorify your Father which is in heaven.

Not that they may glorify you, but that they may glorify your Father who is in heaven.

5:17 Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfil.

Think not that I am come to destroy the law - Do not imagine that I am come to violate the law καταλυσαι, from κατα, and λυω, I loose, violate, or dissolve - I am not come to make the law of none effect - to dissolve the connection which subsists between its several parts, or the obligation men are under to have their lives regulated by its moral precepts; nor am I come to dissolve the connecting reference it has to the good things promised. But I am come, πληρωσαι, to complete - to perfect its connection and reference, to accomplish every thing shadowed forth in the Mosaic ritual.

5:18 For verily I say unto you, Till heaven and earth pass, one jot or one tittle shall in no wise pass from the law, till all be fulfilled.
No cross of a “t” and no dot of an “I” shall be taken from God’s law. Its requirements will always be the same; immutably fixed, and never to be abated by so little as “one jot or one tittle.”

5:19 Whosoever therefore shall break one of these least commandments, and shall teach men so, he shall be called the least in the kingdom of heaven: but whosoever shall do and teach them, the same shall be called great in the kingdom of heaven.
Whosoever therefore shall break one of these least 

commandments - Which are to be understood 

---not of the beatitudes in the preceding verses, for these were not delivered by Christ under the form of commandments; 

---nor of any of the peculiar commands of Christ under the Gospel dispensation; 

---but of the precepts of the law, and might be said to be broke, loosed, or dissolved, as the word here used signifies, when men acted contrary to them.

5:20 For I say unto you, That except your righteousness shall exceed the righteousness of the scribes and Pharisees, ye shall in no case enter into the kingdom of heaven.

that except your righteousness exceed the righteousness of the Scribes and Pharisees, ye shall in no wise enter into the kingdom of heaven. - He mentions the Scribes, because they were the more learned part of the people, who were employed in writing out, and expounding the law; and the Pharisees, because they were the strictest sect among the Jews for outward religion and righteousness; and yet, it seems, their righteousness was very defective; it lay only in an external observance of the law; did not arise from a purified heart, or the principles of grace.

Chapter 5: 1-12 Sermon on the Mount; The Beatitudes

5:1 And seeing the multitudes, He went up into a mountain: and when He was set, His disciples came unto Him:
And seeing the multitudes - At some distance, as they were coming to him from every quarter. He went up into the mountain - Which was near: where there was room for them all.
He went up into a mountain - That he might have the greater advantage of speaking, so as to be heard by that great concourse of people which followed Him. It is very probable that nothing more is meant here than a small hill or eminence.

5:2 And He opened His mouth, and taught them, saying,
And He opened His mouth - He spoke with a clear and strong voice, that all the people might hear Him; and with great freedom, utterance, and cheerfulness, and things of the greatest moment and importance; and taught them; not His disciples only, but the whole multitude.

5:3 Blessed are the poor in spirit: for theirs is the kingdom of heaven.
“Blessed.” See how Jesus begins His Sermon on the Mount, He begins with benedictions. He is a cloud that is full of rain, and that empties itself upon the earth.
Blessed are the poor in spirit, etc. - Or, happy, μακαριοι from μα or μη, not, and κηρ, fate, or death.

5:4 Blessed are they that mourn: for they shall be comforted.

Let them be comforted now in the prospect of future comfort. There are no mourning hearts that mourn over sin, and mourn after God, that shall be deserted by their God: “they shall be comforted.”

5:5 Blessed are the meek: for they shall inherit the earth.

Blessed are the meek - Happy, οι πραεις, from ῥαος, easy, those who are of a quiet, gentle spirit, in opposition to the proud and supercilious Scribes and Pharisees and their disciples.

They shall inherit the earth; it is quoted from Psalm 37:11. They shall inherit the land (so it may be read), the land of Canaan, a type of heaven. So that all the blessedness of heaven above, and all the blessings of earth beneath, are the portion of the meek.

5:6 Blessed are they which do hunger and thirst after righteousness: for they shall be filled.
They want to be better; they are hungry and thirsty after more holiness. They boast not of personal perfection, they are hungering and thirsting after righteousness.

5:7 Blessed are the merciful: for they shall obtain mercy.

The merciful - The tender - hearted: they who love all men as themselves: They shall obtain mercy - Whatever mercy therefore we desire from God, the same let us show to our brethren. He will repay us a thousand fold, the love we bear to any for His sake.

5:8 Blessed are the pure in heart: for they shall see God.

Blessed are the pure in heart - Not in the head; for men may have pure notions and impure hearts; not in the hand, or action, or in outward conversation only; so the Pharisees were outwardly righteous before men, but inwardly full of impurity; but "in heart".

5:9 Blessed are the peacemakers: for they shall be called the children of God.
The peace makers - They that out of love to God and man do all possible good to all men.
They shall be called the children of God - it will be an evidence to themselves that they are so; 

God will own them as such, 

and herein they will resemble Him.

5:10 Blessed are they which are persecuted for righteousness' sake: for theirs is the kingdom of heaven.
They which are persecuted - Δεδιωγμενοι, they who are hard pressed upon and pursued with repeated acts of enmity.

for righteousness sake - on account of their righteous and godly conversation, which brings upon them the hatred and enmity of the men of the world:

5:11 Blessed are ye, when men shall revile you, and persecute you, and shall say all manner of evil against you falsely, for My sake.
Blessed are ye when men shall revile you -These words are particularly directed to the disciples of Christ, and are designed to inform them, that they should not be exempted from reproach and persecution, and to animate and fortify them against it; and are prophetical of what they, and the first Christians particularly, were to endure for Christ's sake.

5:12 Rejoice, and be exceeding glad: for great is your reward in heaven: for so persecuted they the prophets which were before you. 

Rejoice and be exceeding glad - Because of the honor put upon them, the glory they bring to Christ and His cause, by cheerfully suffering for it; and because of the glory and happiness that shall follow upon their sufferings:
Your reward - Even over and above the happiness that naturally and directly results from holiness.
for so persecuted they the prophets which were before you - as Isaiah, Jeremiah, Zechariah, and others; 

which shows, that what should befall them was no new and strange thing, but what had been the lot of the most eminent servants of God in former ages.