[Sorry, another long post, but may as well write them as they occur to me--otherwise they're gone.]
You may wonder why I tend to go on so about detachment. Putting aside the fact that it is absolutely central to all of the teachers (and Doctors of the Church) within my Order, there are good and proper reasons for thinking about detachment and taking steps to become detached.
In all of my reading of the lives of the Saints the central theme is one of self-giving love. For one to be able to be self-giving, one must not be too strictly tied down or restricted in motion. One cannot give oneself if one is not free to do so.
Jesus told us, "You cannot serve God and mammon." His statement was not strictly about money, but about split allegiances. You cannot serve two masters. When you are attached to things you are serving the master of self-interest while trying to serve God. These two, while not always diametrically opposed do often tend to take different forks in the road. You cannot travel two paths.
St. Thomas Aquinas has a long discussion of the simplicity of God (practically the only thing from the Summa that I think I grasp). In it, he ultimately proves that God is simple, speaking in the terms of the time, He is of one substance and mind. How can anything that is duple (or worse) hope to unite with what is simple and single? It can happen via miracle, but God prefers methods that are not so invasive of creation and of personal sovereignty. And personal sovereignty, make no doubt of it, is what God is asking us to surrender. We are to give Him rule of our lives. If we are being pulled this way and that by creation, we cannot be drawn as swiftly to the creator.
Detachment is a means to an end. It is a necessary means, but in no way a sufficient means. Grace, sacraments, prayer, and many other attainments of a life lived in accord with God's will are required. But without detachment, all of these other things will not bring one to Union with God--the ultimate aim of all Christians, and an end that is within the grasp of all at God's good pleasure. Every Saint teaches detachment in one way or another, either through their writings or through their practice and the lives that they lived.
Detachment is not easy but it is very simple. On our own it is impossible, with Christ it becomes possible. It is "simply" a matter of learning to live as St. Paul described when he said, "I know how to be rich and I know how to be poor." That is, your state in life becomes meaningless because all meaning is invested in the centrality of God.
Detachment is not easy for several reasons. First, we often don't recognize attachments. Second, even when we recognize them, we often rationalize them. An example--I was in an extended Ignatian Retreat with a gentleman who was very devoted to the Rosary. The retreat master laid out the rules in the first session--there would be no spiritual reading material other than the Ignatian Exercises, the Holy Bible, and The Imitation of Christ. All other habitual devotions should be put aside for the duration of the retreat so that energy could be focused on the intense retreat exercises. The gentleman asked about the Rosary, and while the good Priest praised the devotion, he discouraged it for the duration of the exercise. The gentleman did not return. Now, this could well be a case in which the man discerned through this mechanism that he was not called to the retreat, but equally likely, it could be an example of an attachment getting in the way of a good that could draw one on toward God. I cannot know that, but proper discernment by the person involved could show which was true.
Third, even when we do not rationalize and we do recognize, sometimes we simply do not wish to give up the object, idea, or practice to which we are attached. This is typified by St. Augustine's famous prayer, "Lord make me chaste, but not just yet." Yes, Lord, I want sanctity, but not as much as I want ___________. And the things that fill in the blank vary from person to person.
The first step toward union with God is recognizing that our entire lives are meaningless without it. When we finally come to terms with the fact that God is our meaning and He is the only thing that will completely fill the empty spaces we try to cram with all manner of junk, then we can begin down the proper road. In other words, when love of God takes priority, detachment from things becomes a possibility, but not until then. And detachment is only a means--it must happen, but it doesn't happen necessarily by focusing on it. In some really tough cases, you might have to concentrate energy, prayer, and resources on becoming detached. But detachment is often a natural corollary of loving something else more. I have no difficulty choosing between say flan and chocolate because I have a built-in liking for chocolate. The choice becomes easy. When you prefer God to all other things, it becomes a matter of making choices that reflect that preference--detachment has begun.
Detachment is also somewhat like Zen. If you become aware that you are practicing it, you almost undo its effects through pride and through the idea that YOU are practicing it. Yes, your will is involved and you are actively doing something, but God and the Holy Spirit within you are more important in the overall efficacy. Here again a statement of Jesus applies in context, "Do not let the right hand know what the left hand is doing." Detachment is most effective when you are detached from doing it and its effects.
However, as I pointed out, sometimes it is sufficiently to light wash and rinse the pan, at other times one needs steel wool or scouring pad. At these times, a deliberate, prayer-infused, sacrament-powered pursuit of detachment is called for. Put in the proper context, it is amazing what one person can do. My father-in-law went for a medical checkup one day and the doctor informed him that cigarette-smoking was shortening his life and interfering with his health. He could choose between cigarettes and unassisted breathing. He went home, dumped the cigarettes and never again took a puff. A truly remarkable instance of the power of really making a choice.
So, detachment is necessary--but it is a means that should not be a focus. Detachment comes very naturally when the things to which one is attached are not valued as much as something else. So the next step is to think about the cultivation of active, responsive, all-encompassing love of God.