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.
Commentary on Matt 5:1-12; Luke 6:20-26