"The soul is first and foremost a being filled with longing. It is filled with sympathy and antipathy, with the world of wishes, of desire. After some time however, the spirit reveals to the soul that it comprises more than only desire. When the soul, led by the spirit, has overcome the longing, then she is not passive, then love flows from the evolved soul, in the same way that longing flows from the undeveloped soul. Desire and love, these are the two opposing forces between which the soul develops. The soul still trapped in sensuality, in outward appearance, is the soul filled with longing; the soul that that has evolved its relationship, its harmony with the spirit, is the loving soul. That is what leads the soul on its path from incarnation to incarnation, in that it evolves from being filled with longing and desire, into a loving soul whose activities become actions of love."
Source (German): Rudolf Steiner – GA 52 – Spirituelle Seelenlehre und Weltbetrachtung – Berlin, March 8, 1904 (page 347)