And opening his mouth, he taught them, saying:

“"Seeing the crowds, Jesus." Here the Lord sets forth his teaching, and this is divided into three parts. In the first is set down the teaching of Christ; in the second is set down the power of the teaching; in the third, the end to which it leads. The second is at chapter 13; the third at chapter 17. The first is divided into three. In the second, the ministers of the teaching are instructed; in the third, the adversaries are confounded. The second is at chapter 10; the third at chapter 11. The first is divided into two. In the first, the teaching of Christ is set forth; in the second, it is confirmed by miracles, at chapter 8. The first into two. In the first, a kind of title is prefixed to the teaching; in the second, the teaching itself is explained, at "Blessed are the poor in spirit." Concerning the first he does three things. First he describes the place where the teaching was set forth; second, the hearers of the teaching; third, he sets down the manner of teaching. The second at "and when he had sat down"; the third at "and opening his mouth he taught them." He says therefore — as I said, that they followed, etc. "Seeing the crowds, Jesus." This text can bear a twofold understanding. First, thus: he went up in order to teach the crowds, that is, not fleeing them. Hence Chrysostom says that just as a craftsman, when he sees the material prepared, delights to work, so the priest delights to preach when he sees the people gathered together; and therefore, "he went up"; Psalm 34:18: "I will confess to you in the great Church." Or otherwise: "he went up," namely fleeing the crowds, so as to teach the disciples more securely; Ecclesiastes 9:17: "the words of the wise are heard in silence." And it should be noted that we read that Christ had three refuges: for at times he fled to the mountain, as is said here, and John 8:1: "And Jesus went to the Mount of Olives." At other times to a boat; Luke 5:1: "when many crowds pressed upon him... going up into one boat, which was Simon's... sitting he taught." The third, into the desert; Mark 6:31: "let us go apart into the desert." And this is fitting enough; for in three things a man can have refuge in God: in the protection of the divine height, which is signified by the mountain; Psalm 124:1: "they who trust in the Lord are as Mount Zion." In ecclesiastical fellowship, which is designated by the boat; Psalm 121:3: "Jerusalem, which is built as a city, whose participation is in itself." In the solitude of religious life, which is taken through the desert, through contempt of temporal things; Hosea 2:14: "I will lead her into solitude, and I will speak to her heart"; Psalm 54:8: "behold, I have gone far off in flight, and I have remained in solitude." Now he went up onto the mountain for five reasons. The first, to show his excellence: for he himself is the mountain of which Psalm 67:16 speaks: "the mountain of God, a fat mountain." The second, to show that the teacher of this doctrine ought to ascend to the eminence of life; Isaiah 40:9: "Get you up upon a high mountain, you who bring good tidings to Zion." Chrysostom: no one can stand in the valley and speak of heaven, etc. The third reason, to show the height of the Church to which the teaching is set forth; Isaiah 2:2: "the mountain of the house of the Lord shall be on the top of mountains, and shall be exalted above the hills." Fourth, to show the perfection of this teaching, because it is most perfect; Psalm 35:7: "your justice is like the mountains of God." Fifth, so that it might correspond to the old legislation, which was given on a mountain; Exodus 19 and 24. Consequently the hearers are set down: "and when he had sat down, his disciples came to him." Two things can be noted in his sitting. Humiliation; Psalm 138:2: "you have known my sitting down." When he was in the height of the divine majesty, his teaching could not be grasped; but then men began to grasp it, when he humbled himself. Or this pertains to the dignity of the office of teacher; below, 23:2: "the Scribes and Pharisees have sat on the chair of Moses." For quiet is required for the pursuit of wisdom. "His disciples came to him," etc., not only in body but in mind; Psalm 33:6: "come to him, and be enlightened"; Deuteronomy 33:3: "they who draw near to his feet shall receive of his teaching." And note that when the Lord preached to the crowds, he stood; Luke 6:17: "Jesus, coming down from the mountain, stood in a level place"; but here, when teaching the disciples, he sat. From this arose the custom that preaching to crowds is done standing, and to religious, sitting. "And opening his mouth he taught them." Here the manner of the teaching is set down. In his saying "opening," it is signified that he had been silent for a long time before. And it shows that he was about to make a great and long sermon, as Augustine says. Or that he was about to say great and profound things; for so men are accustomed to do; Job 3:1: "after this Job opened his mouth, and cursed his day." And he says "his own mouth": for before he had opened the mouths of the prophets; Wisdom 10:21: "wisdom opened the mouth of the dumb, and made the tongues of infants eloquent": for he himself is the wisdom of the Father. But here there is a question: for this sermon is set down, as to many points, also at Luke 6:20ff. But there seems to be a contrariety between here and there, as is evident in the text. And Augustine gives two solutions. One is that this is a different sermon from that one: for he first went up onto the mountain, and delivered this sermon to the disciples, and afterward, coming down, he found the crowd gathered, to whom he preached the same things, and recapitulated many of them: and it is of this that Luke 6:20ff. speaks. Or otherwise it should be said that there was one mountain, which had a level place on its side: that level place was raised up by another, smaller hill. Hence the Lord went up onto the mountain, that is, onto the level place of that mountain. And first he went up higher, and called together the disciples, and there he chose the twelve apostles, as is evident in Luke; and afterward, coming down, he found the crowd gathered, and when the disciples came to him he sat down, and delivered this sermon to the crowds and the disciples. And this seems truer: because Matthew says at the end of the sermon that the crowds marveled at his teaching. Nevertheless, whichever is accepted, there is no contrariety.”

“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, who heard him with astonishment; see Mat 7:28. Some things in the following discourse are directed to the disciples in particular, and others regard the multitude in general.”

“Opening his mouth. It is a Hebraism, to signify he began to speak. (Witham) — This is a common expression in Scripture, to signify something important is about to be spoken. Thus it is used in various other places, as “Job opening his mouth cursed his day, and said,” &c. Daniel, chap. x. et alibi. (Jansenius) — And why is it added, says St. Chrysostom “and opening his mouth,” without doubt that we might know, that not only when he spoke, but even when silent, he gave instruction: sometimes, therefore, he opened his mouth; at other times he spoke by his very actions. (Hom. xv.)”