What is an abyss of naturalism? It is the hole that swallows up any meaningful statement of morality, meaning, or even in the final analysis, basis for belief in rationality. It is quite amusing to watch the naturalists prate about the bad ethics of creationists (some of the statements of creationists ARE quite bad), when naturalism reduces all ethics to personal choice. People without a worldview firmly rooted in the concept of an immanent and transcendent creator - God have "both feet planted firmly in the air" when it comes to meaning, morals, epistemology, and even their precious "laws of science." The last of these is particularly amusing to watch, as you try to help the dunderheads realize that there is no POSSIBLILTY of "laws of science" without the concept of transcendent absolutes. There is statistical probablility, and nothing more. Moreover, even that probabilility, given the expanse of the universe and the tiny bit of knowledge we have about it, is fairly shitty. These people remind me of little children who cover their eyes with their hands and then declare that you are not there because you are outside their field of vision.
The "abyss of naturalism" is the hole that eventually swallows science itself.