The Gospel of Matthew
Gaebelien: "Introduction to Matthew, Chapter 5”
In Chapters five through seven we have the full report of the so-called Sermon on the Mount. Mark and Luke give fragments of this discourse, but the complete discourse is found only in Matthew. The Sermon on the Mount is the proclamation of the King concerning His Kingdom, and may well be called the "Magna Charta of the Kingdom of Heaven."
The beatitudes give the character of the heirs who enter the Kingdom. They do not speak of what a person should be, or strive to be, but what they are. Only the Grace of God can produce such a character. The blessings are in possession of those, who have believed on the Son of God. And the Lord Jesus manifested all these characteristics in His humiliation. But these beatitudes have also a significance in connection with the future believing remnant of Israel, waiting amidst the great tribulations and under the severest persecutions at the end of the age for the return of the King.
The Law is then taken up by the King in this proclamation. He is the Lawgiver and therefore He confirms, expands, and supplements the Law. The better righteousness needed to enter the Kingdom is not man's own righteousness, but that which is by faith in Jesus Christ. As He speaks with authority He uncovers the heart of man and shows the depths of corruption and the hopelessness that the natural man could ever attain such a righteousness. The words of the King condemn every man and prove him lost. The condemnation of the natural man is written here.
 Gaebelein, Arno C. (c. 1970). "The Holy Scriptures Analyzed and Annotated: Matthew" - Moody Press, Loizeaux Bothers