Ultimately, committed agnostics must be committed pragmatists. Because they confess to an eternal inability to know the truth about God, they must make decisions based on what can be absolutely proved by the evidence. From the New Dictionary of Theology:
...agnosticism is based on an ethic of belief which requires that only those propositions should be believed for which there is sufficient evidence...Agnosticism in fact, if not in name, is one consequence of Kant's arguments about human knowledge being bounded by the categories of time and space. God, beyond time and space, is the unknowable.
Thus, agnostics are determined to deal with the knowable. Which begs the question of our agnostic friends: How is morality knowable to you? Our letter-writer is right in saying that we shouldn't assume that morality is limited to Christians. Problem is, he's borrowing from a Biblical thought-system when he even brings up the issue of morality. One way to go, then, would be to press him on his idea of morality: What is right and good? What makes right and good, right and good? If he's consistent, his morality must be based on pragmatism, on what works...which leads down another fun trail. Now from R.C. Sproul, Jr.'s Tearing Down Strongholds:
The problem with pragmatism as an epistemology - with deciding that truth should be determined by what works best - is that it just doesn't work. It begins with an impossible teleological hill to climb. It cannot answer the obvious question, "Works for what?" How do we answer this question without already having a true standard of what our goal is?...There is no route available to the pragmatist to discover what route we all should be on...Pragmatism is, in short, amoral. It cannot provide any sort of ethic at all.
After this, then, what do we do? If we are able to expose the folly of pragmatism, thus the emptiness of agnosticism, where have we left him? After we tear down a stronghold, we must build up the stronghold of the gospel in his eyes. We might give this man our testimony of God's grace triumphing over our. We might tell him of Jesus' statement that He came for the sinners, not for the righteous. Ultimately, my neighbor's problem isn't agnosticism, it's self-righteousness. He believes himself to be a good, moral person. As long as he believes this, he will have no need for Christ. What he needs is to see how he measures up (or doesn't) to God's law and the greatness of a religion that's based on what another's done, not what we do.
Tim Keller has commented before that Christianity, distinct from all other religions, isn't spelled D-O. It's not about what we do. It's spelled D-O-N-E; it's about what Christ has done in our place. This is what my neighbor needs to hear!
Here's what my dad wrote:
Christianity isn't about outward appearances. It's about the new creation within. No matter how good we look on the outside, we can never be anything but "whitewashed sepulchres" if God hasn't regenerated us.
It's true that the Christian's every thought and action should be captive to the will of our Saviour and that the world IS watching us. But it's also true that we recognize that we will stumble and fall and that we have a heavenly Father who is faithful and just to forgive our sins.
So I guess my response to the gentleman who wrote the letter is yes, those who have a faith and love for God are not the only ones who may have a moral compass. My only questions is this: without God, ultimately, in what direction is this gentleman's moral compass pointing?