14 However, in the face of this satanic hatred of religion, which reminds Us of the "mystery of iniquity" ( Thess . ii. 7) referred to by St. Paul, mere human means and expedients are not enough, and We should consider ourselves wanting in Our apostolic ministry if We did not point out to mankind those wonderful mysteries of light, that alone contain the hidden strength to subjugate the unchained powers of darkness. When Our Lord, coming down from the splendors of Thabor, had healed the boy tormented by the devil, whom the disciples had not been able to cure, to their humble question: "Why could not we cast him out?" He made reply in the memorable words: "This kind is not cast out but by prayer and fasting" ( Matth . xvii. 18, 20). It appears to Us, Venerable Brethren, that these divine words find a peculiar application in the evils of our times, which can be averted only by means of prayer and penance.
Source: Caritate Christi Compulsi (Vatican.va)