To Purify the Soul
At a certain point in the spiritual journey God will draw a person from the beginning stage to a more advanced age. At this stage, the person will begin to engage in religious exercises and grow deeper in the spiritual life.
Such souls will likely experience what is called the “dark night of the soul.” The “dark night” is when those persons lose all the pleasure that they once experienced in their devotional life. This happens because God wants to purify them and move them on to greater heights.
After a soul has been converted by God, that soul is nurtured and caressed by the Spirit. Like a loving mother, God cares for and comforts the infant soul by feeding it spiritual milk. Such souls will find great delight in this stage. They will begin praying with great urgency and perseverance; they will engage in all kinds of religious activities because of the joy they experience in them.
But there will come a time when God will bid them to grow deeper.
John of the Cross (1542-1591), excerpt from The Dark Night of the Soul