St. John of the Cross make the point that sensual attractions are so strong and so rooted in our nature that efforts of renunciation by themselves will not be totally successful. A greater attraction, a greater love has to inflame us in order to enable us to let go of lesser, disordered loves.
A love for pleasure, and attachment to it, usually fires the will toward the enjoyment of things that give pleasure. A more intense enkindling of another, better love (love of the soul's Bridegroom) is necessary for the vanquishing of the appetites and the denial of this pleasure. By finding satisfaction and strength in this love, it will have the courage and constancy to readily deny all other appetites. The love of its Bridegroom is not the only requisite for conquering the strength of the sensitive appetites; and enkindling with urgent longings of love is also necessary. For the sensory appetites are moved and attracted toward sensory objects with such cravings that if the spiritual part of the soul is not fired with other, more urgent longings for spiritual things, the soul will be able neither to overcome the yoke of nature nor to enter the night of sense; nor will it have the courage to live in the darkness of all things by denying its appetites of them... How easy, sweet, and delightful these longings for their Bridegroom make all the trials and dangers of this night seem. - St. John of the Cross