I have noticed a lot of comments lately in articles referring to suffering by persons as they are going through a "dark night of the soul". I have heard it expressed by inmates who are depressed and suffering, too. Understanding our soul is to understand our interior life. Since, our interior life is not separate and our exterior life is dependent on the sanctification of our interior life or soul, we must be clear about what it means to refer to "the dark night of the soul".
St. Theresa of Avila wrote in "Interior Castle" that we must be educated about our soul. Martin Luther is an example of what not to believe about the soul. Martin Luther chose to align his beliefs with the philosophical presupposition of the separation of the soul and body. That what we do cannot cause merit in the body. Hence, he created on a widespread basis a sort of belief in "dualism" or expressing that the interior life and exterior life are not interdependent. This "interdependence" was expressed in Dom Chautards work, The Soul of the Apostolate.
With all sanctification of the soul, it is the action and work of God. His power to work in our soul is by His grace. We cannot do anything to bring the power of His Grace into our soul. We can only dispose ourselves to be open to the graces He wishes to give us. Which is very important, because we do not want to live a moment without the graces He wishes to give us. But, we have to know He has them for us. That is why the faithful have the Church to teach them about the work of God in their interior and exterior lives. Without the Church, there would be not authority or assurance or knowledge of what God's promises are and how He keeps them.
Prayer is how we dispose ourselves to be open to receive the power of His graces to sanctify our souls. Then we must be obedient to those graces. When can know when and how God is working in our life, again, by what His Son has revealed to mankind via the instrument of His Church. We can know, interiorly, by what is referred to as our "conscience" what is right and what is wrong when it comes to the "moral absolutes". God outlined them for us in His Decalogue, or Ten Commandments that he gave to Moses. So, even though man could know that there were false gods, that adultery and murder were wrong, He spelled it out for us so we could have more freedom to know the Truth. But, as St. Paul said, they "were written on our hearts", now that they were given to us, "sin entered the world". We became culpable or answerable to God for disobeying His Ten Commandments.
But, for the Jews, under the Old Covenant, the sanctification of the soul was not possible. It wasn't until Christ came into the world Redeemed us in body and spirit and gave us the fulfillment of Revelation, in the New Covenenat that we could know about our soul. Christ wants us to know that our soul is the closest thing to His Father, so if we love God with all our hearts, soul and mind, we must listen to the Church who explains to us through the mystics and the Saints how to be obedient to the graces God gives us, so our soul will become holier. The goal of the Christian life is to be in communion with God. It is a journey. The Sacraments help us on this journey, but there is a profound communion with God that the soul does not experience, until God gives this grace to the soul.
This grace of Communion with God is outlined in St. Theresa of Avila's, Interior Castle. In her work, communion with God is a union that happens after the soul goes through five stages of sanctification. Even at the sixth and seven stages which she writes concerning the experiences of the soul that reaches union with God, it is a grace that God gives the soul. We must desire to be in union with God, but not search it out or try to make it happen. We should only love God and desire for us whatever He wills.
Let's now be clear about what the "dark night of the soul" is. There can be a time on the soul’s journey to communion with God, that the soul will experience what is referred to as "the dark night". It has most recently been publicized the most with the advent of the book about Mother Teresa's dark night of the soul. Her "dark night" has been extensively misunderstood. The atheists say, "see that proves there is no God" and the faithful, think, "yes, that is why I am depressed". But, this dark night is not a feeling that comes from a sad subjective emotional experience. It is an experience of a "knowing" in the soul that God is not there or is absent. In the same way that we "know" for sure the Truths about God and His existence and love, "knowing" that God is absent is something that cannot be explained to other people. When God is absent, you just know it. It is not something you feel, it is something you know. The thing about this "dark night" and loss of God is that the soul is still moved to adore God because even though it feels that God has abandoned it, it still interiorly knows the promises that God gave the world are being kept by Him, but in a special way for the soul who no longer feels the presence of God. There may be a feeling of a lack of faith, but, since the soul still prays and strives to do God's will, faith is still active. Afterall, it is a virtue infused in our soul when we are created and activated at our Baptism, so if one does not pray, and is a sinner, one can feel they have lost faith. But, in all reality, it is still there, in their soul, they just need to repent, encounter Christ's love and faith will be restored.
In Mother Teresa's soul, sin was not want made her feel an abandonment of God. It was evidence of God's plan to bring her closer to Himself. On the soul’s journey to God, the "dark night" can eventually take the soul into a union so profound that with God, that the soul experiences Him more intimately than the soul ever would have, had it not gone through "the dark night."