The Secret to Spiritual growth

God generally sends these storms and trials in this sensory night and purgation to those whom he will afterward put in the other night - although not all pass on to it - so that thus chastised and buffeted, the senses and faculties may gradually be exercised, prepared, and inured for the union with wisdom that will be granted there. For if a soul is not tempted, tried, and proved through temptations and trials, its senses will not be strengthened in preparation for wisdom. It is said therefore in Ecclesiasticus: He who is not tempted, what does he know? And he who is not tried, what are the things he knows? [Ecclus. 34:9-10]. Jeremiah gives good testimony of this truth: You have chastised me, Lord, and I was instructed [Jer. 31:18]. And the most fitting kind of chastisement for entering into wisdom consists of the interior trials we mentioned, since they most efficaciously purge the senses of all the satisfaction and consolation the soul was attached to through natural weakness. By these trials it is truly humbled in preparation for its coming exaltation.

St. John of the Cross, Book 1.14.4

Commentary: In simple words, there is no gain without pain. Our common American Christian teaching is that we can have all of God's blessings with no suffering. There is no greater heresy.