Summary: A classic sermon by St. Augustine on the Sermon on the Mount in Matthew 5.
1. If any one will piously and soberly consider the sermon which our Lord Jesus Christ spoke on the mount, as we read it in the Gospel according to Matthew, I think that he will find in it, so far as regards the highest morals, a perfect standard of the Christian life: and this we do not rashly venture to promise, but gather it from the very words of the Lord Himself. For the sermon itself is brought to a close in such a way, that it is clear there are in it all the precepts which go to mould the life. For thus He speaks: “Therefore, whosoever hears these words of mine, and does them, I will liken him unto a wise man, which built his house upon a rock: and the rain descended, and the floods came, and the winds blew, and beat upon that house; and it fell not: for it was founded upon a rock. And every one that hears these words of mine, and does them not, I will liken unto a foolish man, which built his house upon the sand: and the rain descended, and the floods came, and the winds blew, and beat upon that house; and it fell: and great was the fall of it.” Since, therefore, He has not simply said, “Whosoever hears my words,” but has made an addition, saying, “Whosoever hears these words of mine,” He has sufficiently indicated, as I think, that these sayings which He uttered on the mount so perfectly guide the life of those who may be willing to live according to them, that they may justly be compared to one building upon a rock. I have said this merely that it may be clear that the sermon before us is perfect in all the precepts by which the Christian life is moulded; for as regards this particular section a more careful treatment will be given in its own place.
2. The beginning, then, of this sermon is introduced as follows: “And when He saw the great multitudes, He went up into a mountain: and when He was set, His disciples came unto Him: and He opened His mouth, and taught them, saying.” If it is asked what the “mountain” means, it may well be understood as meaning the greater precepts of righteousness; for there were lesser ones which were given to the Jews. Yet it is one God who, through His holy prophets and servants, according to a thoroughly arranged distribution of times, gave the lesser precepts to a people who as yet required to be bound by fear; and who, through His Son, gave the greater ones to a people whom it had now become suitable to set free by love. Moreover, when the lesser are given to the lesser, and the greater to the greater, they are given by Him who alone knows how to present to the human race the medicine suited to the occasion. Nor is it surprising that the greater precepts are given for the kingdom of heaven, and the lesser for an earthly kingdom, by that one and the same God, who made heaven and earth. With respect, therefore, to that righteousness which is the greater, it is said through the prophet, “Your righteousness is like the mountains of God:” and this may well mean that the one Master alone fit to teach matters of so great importance teaches on a mountain. Then He teaches sitting, as behooves the dignity of the instructor's office; and His disciples come to Him, in order that they might be nearer in body for hearing His words, as they also approached in spirit to fulfil His precepts. “And He opened His mouth, and taught them, saying.” The circumlocution before us, which runs, “And He opened His mouth,” perhaps gracefully intimates by the mere pause that the sermon will be somewhat longer than usual, unless, perchance, it should not be without meaning, that now He is said to have opened His own mouth, whereas under the old law He was accustomed to open the mouths of the prophets.