Spiritual desire is the drive that God put in us from the beginning, for total satisfaction, for home, for heaven, for divine union, and it just got displaced onto the wrong object.

You stir man to take pleasure in praising you, because you have made us for yourself, and our heart is restless until it rests in you.1

since our hearts are made to find their end in God, we will experience a besetting anxiety and restlessness when we try to love substitutes.