3 For there is nothing whatever that will be able to afflict one who is well ordered in mind, and careful about his own soul; but he will enjoy a pure and continued pleasure. And that this is true you have today heard from Paul, who exhorts us, saying, “Rejoice in the Lord always, and again I say, rejoice.” I know indeed that to many this saying seems impossible. “For how is it possible,” says some one, “that he who is but a man, can continually rejoice? To rejoice is no hard matter, but to rejoice continually, this seems to me to be impossible.”
For many are the causes of sadness, which surround us on all sides. A man has lost either a son, or a wife, or a beloved friend, more necessary to him than all kindred; or he has to sustain the loss of wealth; or he has fallen into sickness; or he has to bear some other change of fortune; or to grieve for contemptuous treatment which he did not deserve; or famine, or pestilence, or some intolerable exaction, or circumstances in his family trouble him—nay, there is no saying how many circumstances of a public or private nature are accustomed to occasion us grief.
How then, he may say, is it possible to “rejoice always?” Yea, O man! It is possible; and if it were not so, Paul would not have given the exhortation; nor would a man endowed with spiritual wisdom have offered such counsel; and for this reason I have constantly said to you, and will not cease to say, that what ye could no where have learned from any other, that wisdom ye may here meditate. For mankind are universally desirous of pleasure, and of rejoicing; and for this, they do all, say all, and undertake all things.
Therefore it is, that the merchant goes on a voyage, in order that he may amass wealth; and he amasses wealth, to the end that he may rejoice over what he has treasured up. The soldier also for this reason exercises his warfare, and the husbandman his husbandry; for this each man plies his art. Those also who love dominion, love it for this end, that they may obtain glory; and they desire to obtain glory, that they may rejoice; and any one may perceive that each of our undertakings is directed to this point, and that every man looking to this makes haste to go towards it through a variety of means.
Source: Homilies on the Statues (New Advent)