10 Since therefore those who are scourged are more blessed than the scourgers, and those in tribulation among us than those who are free from it outside the Christian pale; and those who are sad are more blessed than those in pleasure; what further source of tribulation shall we have? On this account we should call no man happy, save him only who lives according to God. These only the Scripture terms blessed. For “blessed,” it is said, “is the man who has not walked in the counsel of the ungodly.
Blessed is he whom You chasten, and teachest him out of Your law. Blessed are the undefiled in the way. Blessed are all they who trust in Him. Blessed is the people whose God is the Lord. Blessed is he whom his soul condemns not. Blessed is the man that fears the Lord.” And again, Christ speaks thus: “Blessed are they that mourn; blessed are the humble; blessed are the meek; blessed are the peacemakers; blessed are they who are persecuted for righteousness' sake.” Do you see how the divine laws everywhere pronounce blessed none of the rich, or of the well-born, or of the possessors of glory, but the man who has gotten hold of virtue.
For what is required of us is, that in every thing we do or suffer, the fear of God should be the foundation; and if you implant this as the root, not merely will ease, and honour, and glory, and attention, produce fruits that shall be pleasurable to you; but hostilities also, and calumnies, and contempt, and disgrace, and torments, and all things without exception. And just as the roots of trees are bitter in themselves, and yet produce our sweetest fruits, so, verily, godly sorrow will bring us an abundant pleasure.
They know, who have often prayed with anguish, and shed tears, what gladness they have reaped; how they purged the conscience; how they rose up with favourable hopes! For as I am always saying, it is not the nature of the things, but our disposition, which is wont to make us sad or joyful. If then we can render the latter such as it ought to be, we shall have a pledge for all gladness. And just as, with the body, it is not so much the nature of the air, or the things it meets from without, as its own internal condition, that either injures or assists it, so also it is in the case of the soul; and much more so; for in the one case, there is the necessity of nature; in the other, the whole is seated in the power of choice.
Therefore Paul, when he had endured innumerable evils— shipwrecks, wars, persecutions, plots, the assaults of robbers, and things too numerous to be recounted, dying also daily deaths— was so far from grieving or being discontented, that he gloried, and rejoiced, and said, “I now rejoice in my sufferings, and fill up that which is behind of the afflictions of Christ in my flesh.” And again: “And not only so, but we glory in tribulations.” Now, glorying signifies an extension of pleasure.
Source: Homilies on the Statues (New Advent)