For such is humanity's nature, that may be immersed in the depths of evil and be a slave to sin, yet it can still turn to good. One who is totally surrendered to the Holy Spirit and intoxicated with heavenly things is also capable of turning to evil. It is similar to a woman clothed in tattered rags, starving and dirty. Not without much work does she reach a royal rank and put on the purple and the crown and become the spouse of the king. She may recall in memory her past filth and it may come to her to turn back to that former state. But she, nevertheless, does not wish to return to her past, for that would be sheer stupidity. And it is similar to those who "have tasted the divine grace, have been made partakers of the Spirit" (Heb. 6:4). Unless they are attentive, they can defect and even become worse than they were before when they were worldly minded.
---St. Macarios the Great, Fifty Spiritual Homilies