It's difficult to summarise the article adequately but I'll try. The traditional Christian view sees God's creation as a good thing:
The doctrine of creation presented in the Book of Genesis tells us that the world is good, that human beings receive this world as an undeserved gift, and that this makes them dependent upon their creator and bound in humility to acknowledge this gift with gratitude.
Gnostics, however, reject this outlook as suggesting limits and dependence and see the spirit or will as being "trapped" within such a created world.
Mark Shiffman argues persuasively that one of the fathers of liberal modernity, John Locke, was a gnostic in this sense. A gnostic outlook is assumed, first, in his economic theory:
In chapter five of his Second Treatise, Locke defends the individual right to property by arguing that the entire value of commodities derives from human labor. After reflecting a bit on the complexity of human economic activity, Locke ends up estimating that human labor contributes all but about 1/1000 of the value of things, whereas “Nature and the Earth furnished only the almost worthless materials.” The given world is essentially worthless, except as a source of the raw materials for human making...the attitude of Locke and Marx toward the given world can hardly be described as one exhibiting gratitude and reverence. It’s all what we make of it.
Second, Locke carried over this argument into his theory of the human person. Our own body and mind is worthless raw material until we labour on it through our will:
This is the sense in which Locke understands human beings as being their own individual property. All that they are that is of any value results from the labor they exercise upon themselves. Parents are, at best, the enablers of our self-creation, providing us with the material that is nearly worthless until improved by our own efforts.
In short, just as nature and the earth constitute the worthless world whose value lies in what humans can make of it, so too my body and mind are initially parts of that worthless world. It is when my will reshapes all this and turns it into some embodiment of itself that I lay claim to it. The world as given is essentially worthless, and the value things have results from our laboring to make the worthless material suitable to our wishes. It is the will that imparts value both by determining what will make something valuable and by causing that valuable something to be built up in it.
Pope Benedict (as Cardinal Ratzinger) wrote of Gnosticism that:
Human beings want to understand the discovered world only as material for their own creativity…. Gnosticism will not entrust itself to a world already created, but only to a world still to be created.
I've pointed out before that modern liberals reject most aspects of our created nature, but the one aspect they retain is that of the creative spirit. The argument put forward above helps to explain why liberals would have this focus.