"Oh! If we could but now fully understand how a soul cannot reach the thicket and wisdom of the riches of God, which are of many kinds, without entering the thicket of many kinds of suffering, finding in this her delight and consolation; and how a soul with an authentic desire for divine wisdom, wants suffering first in order to enter this wisdom by the thicket of the cross! Accordingly, St. Paul admonished the Ephesians not to grow weak in their tribulations and to be strong and rooted in charity in order to comprehend with all the saints what is the breadth and height and depth, and to know also the supereminent charity of the knowledge of Christ, in order to be filled with all the fullness of God. The gate entering into these riches of His wisdom is the cross, which is narrow, and few desire to enter by it, but many desire the delights obtained from entering there."
St. John of the Cross, The spiritual canticle, Stanza 36.13. The collected works of St. John of the Cross, trans. Kieran Kavanaugh, O.C.D., and Otilio Rodriguez, O.C.D. (Washington, DC: ICS Publications, Institute of Carmelite Studies, 1973), 549; Cf. Obras de San Juan de la Cruz, ed. Silverio de Santa Teresa, O.C.D., vol. 3, Cantico Espiritual, Biblioteca Mistica Carmelitana 12 (Burgos: Tipografia de «El Monte Carmelo», 1930), p. 403.
I have not yet read The spiritual canticle; I was put onto this by the Office of Readings for the Feast of St. John of the Cross. Astonishing material. I must make this a priority, and indeed re-read the other works, too.