17 Now, the whole secret of this divine philosophy is, that what are called the goods of this mortal life have indeed the appearance of good, but not the reality; and, therefore, that it is not in the enjoyment of them that man can be happy. In the divine plan, so far are riches and glory and pleasure from bringing happiness to man that if he really wishes to be happy, he must rather for God's sake renounce them all: "Blessed are ye poor . . . Blessed are ye that weep now; . . . Blessed shall you be when men shall hate you and when they shall separate you, and shall reproach you and cast out your name as evil" ( Luke vi. 20-22). That is to say, that it is through the sorrows and sufferings and miseries of this life, patiently borne with, as it is right that they should be, that we shall enter into possession of those true and imperishable goods which "God hath prepared for them that love Him" (I. Cor . ii. 9). This most important teaching of our Faith is overlooked by many, and by not a few it has been completely forgotten.
Source: Ad Beatissimi Apostolorum (Vatican.va)