Family, dogs, and the woods: these are Billy's top loves (though the order is certainly debatable). The woods are practically a second home to him, and they offer a peace and serenity that is seriously lacking in the hustle and bustle of town. But don't get too comfy. Where the Red Fern Grows never lets us forget how dangerous nature can be. Near-death experience follows near-death experience, until finally the natural world takes Billy's dogs away.
Nature and God are the same thing in this novel. Billy doesn't distinguish between nature worship and Christianity.
The death of Billy's dogs severs his connection to nature. Without that connection, he can never return to his childhood home.