Since ... 'the kingdom of heaven suffers violence and the violent take it by force' (Mt. 11:12), and it is impossible for the faithful to enter it by any other way, unless they come through the narrow gate of trials and tribulations, the divine oracle rightly commands us, saying: 'Strive to enter by the narrow door' (Lk. 13:24). Again He says, 'By your endurance you will gain your souls' (Lk. 21:19), and, 'Through many tribulations we must enter the kingdom of heaven' (Acts 14:22).