Note: The following covers chapters 5-7.
He then gathers around Him those who were definitively to follow Him in His ministry and His temptations; and, at His call, to link their portion and their lot with His, forsaking all beside.
The strong man was bound, so that Jesus could spoil his goods, and proclaim the kingdom with proofs of that power which were able to establish it.
Two things are then brought forward in the Gospel narrative. First, the power which accompanies the proclamation of the kingdom. In two or three verses,  without other detail, this fact is announced. The proclamation of the kingdom is attended with acts of power that excite the attention of the whole country, the whole extent of the ancient territory of Israel. Jesus appears before them invested with this power. Secondly (chaps. 5-7) the character of the kingdom is announced in the sermon on the Mount, as well as that of the persons who should have part in it (the Father's name withal being revealed). That is, the Lord had announced the coming kingdom, and with the present power of goodness, having overcome the adversary; and then shews what were the true characters according to which it would be set up, and who could enter, and how. Redemption is not spoken of in it; but the character and nature of the kingdom, and who could enter. This clearly shews the moral position which this sermon holds in the Lord's teaching.
It is evident that, in all this part of the Gospel, it is the Lord's position which is the subject of the teaching of the Spirit, and not the details of His life. Details come after, in order fully to exhibit what He was in the midst of Israel, His relations with that people, and His path in the power of the Spirit which led to the rupture between the Son of David and the people who ought to have received Him. The attention of the whole country being thus engaged by His mighty acts, the Lord sets before His disciples-but in the hearing of the people-the principles of His kingdom.
This discourse may be divided into the following parts:--  The character and the portion of those who should be in the kingdom (v. 1-12). Their position in the world (v. 13-16). The connection between the principles of the kingdom and the law (v. 17-48).  The spirit in which His disciples should perform good works (chap. 6:1-18). Separation from the spirit of the world and from its anxieties (v. 19-34). The spirit of their relation with others (chap. 7:1-6). The confidence in God which became them (v. 7-12). The energy that should characterise them, in order that they might enter into the kingdom; not however merely enter, many would seek to do that, but according to those principles which made it difficult for man, according to God-the strait gate; and then, the means of discerning those who would seek to deceive them, as well as the watchfulness needed that they might not be deceived (v. 13-23).
Real and practical obedience to His sayings, the true wisdom of those that hear His words (v. 24-29).
There is another principle that characterises this discourse, and that is the introduction of the Father's name. Jesus puts His disciples in connection with His Father, as their Father. He reveals to them the Father's name, in order that they may be in relation with Him, and that they may act in accordance with that which He is.
This discourse gives the principles of the kingdom, but supposes the rejection of the King, and the position into which this would bring those that were His; who consequently must look for a heavenly reward. They were to be a divine savour where God was known and was dealing, and would be a spectacle to the whole world. Moreover this was God's object. Their confession was to be so open that the world should refer their works to the Father. They were to act, on the one hand, according to a judgment of evil which reached the heart and motives, but also, on the other, according to the Father's character in grace-to approve themselves to the Father who saw in secret, where the eye of man could not penetrate. They were to have full confidence in Him for all their need. His will was the rule according to which there was entrance into the kingdom.
We may observe that this discourse is connected with the proclamation of the kingdom as being near at hand, and that all these principles of conduct are given as characterising the kingdom, and as the conditions of entrance into it. No doubt it follows that they are suitable to those who have entered in. But the discourse is pronounced in the midst of Israel,  before the kingdom is set up, and as the previous state called for in order to enter, and to set forth the fundamental principles of the kingdom in connection with that people, and in moral contrast with the ideas they had formed respecting it.
In examining the beatitudes, we shall find that this portion in general gives the character of Christ Himself. They suppose two things; the coming possession of the land of Israel by the meek; and the persecution of the faithful remnant, really righteous in their ways, and who asserted the rights of the true King (heaven being set before them as their hope to sustain their hearts). 
This will be the position of the remnant in the last days before the introduction of the kingdom, the last being exceptional. It was so, morally, in the days of the Lord's disciples, in reference to Israel, the earthly part being delayed. In reference to heaven, the disciples are looked at as witnesses in Israel; but-while the only preservative of the earth-they were a testimony to the world. So that the disciples are seen as in connection with Israel, but, at the same time, as witnesses on God's part to the world (the kingdom being in view, but not yet established). The connection with the last days is evident; nevertheless their testimony then had, morally, this character. Only the establishment of the earthly kingdom has been delayed, and the church, which is heavenly, brought in. Chapter 5:25 evidently alludes to the position of Israel in the days of Christ. And in fact they remain captive, in prison, until they have received their full chastisement, and then they shall come forth.
The Lord ever speaks and acts as the obedient man, moved and guided by the Holy Ghost; but we see in the most striking manner, in this Gospel, who it is that acts thus. And it is this which gives its true moral character to the kingdom of heaven. John the Baptist might announce it as a change of dispensation, but his ministry was earthly. Christ might equally announce this same change (and the change was all-important); but in Him there was more than this. He was from heaven, the Lord who came from heaven. In speaking of the kingdom of heaven, He spoke out of the deep and divine abundance of His heart. No man had been in heaven, excepting Him who had come down from thence, the Son of man who was in heaven. Therefore, when speaking of heaven, He spoke of that which He knew, and testified of that which He had seen This was the case in two ways, as shewn forth in Matthew's Gospel. It was no longer an earthly government according to the law; Jehovah, the Saviour, Emmanuel, was present Could He be otherwise than heavenly in His character, in the tone, in the essence, of His whole life?
Moreover, when He began His public ministry and was sealed by the Holy Ghost, heaven was opened to Him. He was identified with heaven as a man sealed with the Holy Ghost on earth. He was thus the continual expression of the spirit, of the reality, of heaven. There was not yet the exercise of the judicial power which would uphold this character in the face of all that opposed it. It was its manifestation in patience, notwithstanding the opposition of all around Him and the inability of His disciples to understand Him. Thus in the sermon on the Mount we find the description of that which was suitable to the kingdom of heaven, and even the assurance of reward in heaven for those who should suffer on earth for His sake. This description, as we have seen, is essentially the character of Christ Himself. It is thus that a heavenly spirit expresses itself on earth. If the Lord taught these things, it is because He loved them, because He was them and delighted in them. Being the God of heaven, filled as man with the Spirit without measure, His heart was perfectly in unison with a heaven that He perfectly knew. Consequently therefore He concludes the character which His disciples were to assume by these words: "Be ye therefore perfect, even as your Father in heaven is perfect." All their conduct was to be in reference to their Father in heaven. The more we understand the divine glory of Jesus, the more we understand the way in which He was as man in connection with heaven, the better shall we apprehend what the kingdom of heaven was to Him with regard to that which was suitable to it. When it shall be established hereafter in power, the world will be governed according to these principles, although they are not, properly speaking, its own.
The remnant in the last days, I doubt not, finding all around them contrary to faithfulness, and seeing all Jewish hope fail before their eyes, will be forced to look upward, and will more and more acquire this character, which, if not heavenly, is at least very much conformed to Christ. 
There are two things connected with the presence of the multitude, v. 1. First, the time required that the Lord should give a true idea of the character of His kingdom, since already He drew the multitude after Him. His power making itself felt, it was important to make His character known. On the other hand, this multitude who were following Jesus were a snare to His disciples; and He makes them understand what an entire contrast there was between the effect which this multitude might have upon them, and the right spirit which ought to govern them. Thus, full Himself of what was really good, He immediately brings forward that which filled His own heart. This was the true character of the remnant, who in the main resembled Christ in it. It is often thus in the Psalms.
The salt of the earth is a different thing from the light of the world. The earth, it appears to me, expresses that which already professed to have received light from God-that which was in relationship with Him by virtue of the light-having assumed a definite shape before Him. The disciples of Christ were the preservative principle in the earth. They were the light of the world, which did not possess that light. This was their position, whether they would or no. It was the purpose of God that they should be the light of the world. A candle is not lighted in order to be hidden.
All this supposes the case of the possibility of the kingdom being established in the world, but the opposition of the greater part of men to its establishment. It is not a question of the sinner's redemption, but of the realisation of the character proper to a place in the kingdom of God; that which the sinner ought to seek while he is in the way with his adversary, lest he should be delivered to the judge-which indeed has happened to the Jews.
At the same time the disciples are brought into relationship with the Father individually-the second great principle of the discourse, the consequence of the Son being there-and a yet more excellent thing is set before them than their position of testimony for the kingdom. They were to act in grace, even as their Father acted, and their prayer should be for an order of things in which all would correspond morally to the character and the will of their Father. "Hallowed be thy name, thy kingdom come,"  is, that all should answer to the character of the Father, that all should be the effect of His power. "Thy will be done on earth as it is in heaven" is perfect obedience. Universal subjection to God in heaven and on earth will be, to a certain point, accomplished by the intervention of Christ in the millennium, and absolutely so when God shall be all in all. Meanwhile the prayer expresses daily dependence, the need of pardon, the need of being kept from the power of the enemy, the desire of not being sifted by him, as a dispensation of God, like Job or Peter, and of being preserved from evil.
This prayer also is adapted to the position of the remnant; it passes over the dispensation of the Spirit, and even that which is proper to the millennium as an earthly kingdom, in order to express the right desires, and speak of the condition and the dangers of the remnant until the Father's kingdom should come. Many of these principles are always true, for we are in the kingdom, and in spirit we ought to manifest its features; but the special and literal application is that which I have given. They are brought into relationship with the Father in the realisation of His character, which was to be displayed in them by virtue of this relationship, causing them to desire the establishment of His kingdom, to overcome the difficulties of an opposing world, to keep themselves from the snares of the enemy, and to do the Father's will. It was Jesus who could impart this to them. He thus passes from the law,  recognised as coming from God, to its fulfilment, when it shall be as it were absorbed in the will of Him who gave it, or accomplished in its purposes by Him who alone could do so in any sense whatever.