The "value of life"
Values do pertain to "life" - by definition - but there is no such thing as "the value of life". Life is a prerequisite for ANY discussion of value or morality. We can no more ask why we value life (or death) than we can ask why we use logic. We have no choice but to use logic and we have no choice but to be alive. There is no such thing as "being dead", and there is no "choice", therefore no value and no moral judgment, attached to life.
The Christian, on the other hand, is stuck with life as a choice, because he believes there is more than biological life. So why does the Christian "choose life" (i.e. to be alive) ? It is because of the afterlife belief itself that the Christian is stuck with an intractable problem. He cannot use the same standard as he believes in an afterlife, and whatever theistic standard he uses to validate it has to be circular, because all theistic standards are circular (validity of the Bible, personal revelation, personal experience, evidential theology).
This does not mean that, as Gene Cook tried to argue with me on his message board, that suicide should always be encouraged, or that we should not have this or that value. These are moral issues, and life itself is not a moral issue, so we cannot answer one by using the other. We choose to value this or that part of life, or to encourage our friends to commit or not to commit suicide, but once again we do not choose to be alive or dead.
This conclusion, however, also applies to relativists who ask us to justify our basic adherence to life-affirming principles as objective. Our values are necessarily life-affirming because that is by definition all that we can have needs (and ergo, values) about. So in saying this, the relativist is in fact saying nothing at all. It is not the fact that we value something about life, but rather what we value most in life, that should surprise us.