Nothing lasts. No single thing can consume our entire life’s meaning. No single thing can give us total satisfaction. Nothing is worth everything: neither past, nor present nor future.
To borrow a line from Aristotle, God is the unmoved mover. He does not change. He does not move toward us. It is we who change (a necessary fact from living within Time). It is we who have to move toward God (with the help of the Holy Spirit of course).
It is in this changing, this moving toward God, that we pass through different phases. It is called growth. And as Scripture says, the branches need to be pruned in order for new growth to occur. It is through our struggles, usually painful to some degree, that the pruning occurs. (Sounds like the cup of sorrow and cup of joy.)
Nothing in these phases of life is permanent except God’s presence. And if we are to grow, we should not cling to these different phases of our lives. We must learn from them, apply it to the present as we hope for the future. I think this was the point of Chittister’s article. That is part, but not certainly all, of what detachment means.