Opening his mouth. This redundancy of expression (pleonasmos) partakes of the Hebrew idiom: for what would be faulty in other languages is frequent among the Hebrews, to say, He opened his mouth, instead of, He began to speak. Many look upon it as an emphatic mode of expression, employed to draw attention to any thing important and remarkable, either in a good or bad sense, which has been uttered: but as some passages of Scripture countenance an opposite view, I prefer the former exposition. I shall also dismiss the ingenious speculation of those, who give an allegorical turn to the fact of our Lord teaching his disciples on a mountain, as if it had been intended to teach them to elevate their minds far above worldly cares and employments. In ascending the mountain, his design rather was to seek a retreat, where he might obtain relaxation for himself and his disciples at a distance from the multitude. Now let us see, in the first place, why Christ spoke to his disciples about true happiness. We know that not only the great body of the people, but even the learned themselves, hold this error, that he is the happy man who is free from annoyance, attains all his wishes, and leads a joyful and easy life. At least it is the general opinion, that happiness ought to be estimated from the present state. Christ, therefore, in order to accustom his own people to bear the cross, exposes this mistaken opinion, that those are happy who lead an easy and prosperous life according to the flesh. For it is impossible that men should mildly bend the neck to bear calamities and reproaches, so long as they think that patience is at variance with a happy life. The only consolation which mitigates and even sweetens the bitterness of the cross and of all afflictions, is the conviction, that we are happy in the midst of miseries: for our patience is blessed by the Lord, and will soon be followed by a happy result. This doctrine, I do acknowledge, is widely removed from the common opinion: but the disciples of Christ must learn the philosophy of placing their happiness beyond the world, and above the affections of the flesh. Though carnal reason will never admit what is here taught by Christ, yet he does not bring forward any thing imaginary, -- as the Stoics were wont, in ancient times, to amuse themselves with their paradoxes, -- but demonstrates from the fact, that those persons are truly happy, whose condition is supposed to be miserable. Let us, therefore remember, that the leading object of the discourse is to show, that those are not unhappy who are oppressed by the reproaches of the wicked, and subject to various calamities. And not only does Christ prove that they are in the wrong, who measure the happiness of man by the present state, because the distresses of the godly will soon be changed for the better; but he also exhorts his own people to patience, by holding out the hope of a reward.

(1) And he opened his mouth, and taught them, saying,
(1) Christ teaches that the greatest joy and happiness is not in the conveniences and pleasures of this life, but is laid up in heaven for those who willingly rest in the good will and pleasure of God, and endeavour to profit all men, although they are cruelly vexed and troubled by those of the world, because they will not adapt themselves to their ways.

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 Matthew 7:28. Some things in the following discourse are directed to the disciples in particular, and others regard the multitude in general.

And he opened his mouth--a solemn way of arousing the reader's attention, and preparing him for something weighty. (Job 9:1; Acts 8:35; Acts 10:34).
and taught them, saying--as follows.

Opened his mouth and taught. This wonderful discourse of three chapters is to the New Dispensation what the law given from Sinai was to the Old. That was the moral law of Judaism, this is the moral law of Christianity; that was given from "the Mount that could not be touched," this from the Mount of blessing. Compare Luke 6:20-49.

And he opened his mouth - A phrase which always denotes a set and solemn discourse; and taught them - To bless men; to make men happy, was the great business for which our Lord came into the world. And accordingly he here pronounces eight blessings together, annexing them to so many steps in Christianity. Knowing that happiness is our common aim, and that an innate instinct continually urges us to the pursuit of it, he in the kindest manner applies to that instinct, and directs it to its proper object. Though all men desire, yet few attain, happiness, because they seek it where it is not to be found. Our Lord therefore begins his Divine institution, which is the complete art of happiness, by laying down before all that have ears to hear, the true and only true method of acquiring it. Observe the benevolent condescension of our Lord. He seems, as it were, to lay aside his supreme authority as our legislator, that he may the better act the part of: our friend and Saviour. Instead of using the lofty style, in positive commands, he, in a more gentle and engaging way, insinuates his will and our duty, by pronouncing those happy who comply with it.