What would the world look like if theism or Christianity were true? And what would it look like if naturalism were true—that is, that nature alone explains what we see?
We’re comparing these two worldviews to see which one matches reality best. (Part 1 here.)
Morality
Theism predicts that religion’s moral teachings would be timeless and progressive. The wisdom of heaven might appear crazy to us simple humans, but time after time we’d follow it and discover that it did indeed improve society.
The Bible declares that Christians don’t sin: “No one who is born of God practices sin” (1 John 3:9; see also 3:6, 5:18). With the Christian church run mostly by sinless Christians, the Church’s morality should likewise far outshine that of other institutions.
In fact, Christianity is conservative, not progressive. It is always late to the party, following society after it embraces a new moral outlook. Christianity must be conservative because it is built on the premise that it’s already got things figured out. New ideas—abolition of slavery, democracy, civil rights for all—catch the church off guard. Sometimes the church is mobilized on some of these issues (William Wilberforce against slavery or Martin Luther King for civil rights, for example), but why are these positions not plainly in the Bible? Why did it take close to 2000 years to get on the right side of change? In these examples, the church was merely a tool used by change makers, not the instigator of change.
Christians were on both sides of these moral issues, as is true for any modern moral issue such as same-sex marriage, gay rights, abortion, or euthanasia. Pick the right Bible verses, and God can be used like a puppet and made to support either position. Pick other verses, and God admits to a long list of moral crimes.
As for the church clearly being a morally superior institution, the Catholic Church pedophilia scandal is merely the most recent moral lapse. You can make the bad-apples argument to sacrifice the individuals for the benefit of the institution, but that simply makes a lie of Bible’s claim that Christians don’t sin. The church becomes yet another large club that occasionally abuses power with no special claims of moral superiority over any other—so much for the guiding hand of God.
The Bible has a lot to answer for. The Old Testament in particular supports moral positions—genocide, slavery, polygamy, and human sacrifice, for starters—that modern society has long rejected. No, not all moral positions in the Bible are timeless.
Christianity declares that morality is grounded exclusively in its god, but then it has a hard time explaining why other cultures without Christian dominance, both current and historical, seem to understand morality just fine. The Problem of Evil—the existence of gratuitous evil despite God taking a loving hand in our lives—also argues against Christianity.
Mind
Theism predicts a mind independent of the body that persists as a soul after the body dies.
In fact, “mind” is just what brains do. The mind’s capability is tied to the capabilities of the brain, and that changes as someone grows from child to mature adult to elderly adult. That capability changes due to physical causes such as being tired, sleepy, stressed, hungry, drunk, or drugged. Damage the brain with dementia or physical injury and you damage the mind, as the story of Phineas Gage illustrates. The fortunes of the mind parallel those of the brain, and no evidence supports an unembodied mind.
Not only do we have a natural explanation for the mind, but physics shows that there is no room for a supernatural soul. There is yet more physics to learn, but we know enough about the physics of our world to know that no as-yet-to-be-found quantum particles could hold or convey the soul.
Growth of religion
Theism predicts that heaven would favor the correct religion.
Christianity did thrive, but that wasn’t because of God’s beneficence but Rome’s. Christianity was just one religion among many until the Edict of Thessalonica in 380 CE made Christianity the state religion of the Roman Empire.
Naturalism predicts that religions struggle, rise, and fall and that none will have any supernatural success.
More
If Christianity were true, a single set of moral truths would be held universally, rather than morality being a cultural phenomenon.
If Christianity were true, believers wouldn’t use evidence-based reasoning everywhere in life but then switch to faith for evaluating the claims of their religion.
If Christianity were true, faith healers would go to hospitals and reliably produce healings that science verifies.
If Christianity were true, televangelists wouldn’t waste time asking for money from viewers but would get their expenses covered by praying to God themselves.
If Christianity were true, Christian’s testable prophecies about our imminent end wouldn’t invariably be wrong. (Hilariously bad examples: John Hagee and Harold Camping.)
If Christianity were true, its Bible wouldn’t have contradictions, claims of prophecy wouldn’t suck, and it wouldn’t be wrong about the power of prayer.
If Christianity were true, we wouldn’t see in it mythological themes shared by other contemporary religions of that part of the world like the Combat Myth, virgin birth stories, and dying and rising gods.
If Christianity were true, everyone would understand the same simple and unambiguous message from God.
Christian response
The typical Christian response is, “But God could have perfectly good reasons that make sense to him that you simply can’t imagine!” And that’s true. This tsunami of examples in which the naturalistic explanation beats theism and Christianity doesn’t prove that Christianity is false; it simply concludes that that’s the way to bet. This argument fails by making the Hypothetical God Fallacy.
Cosmologist Sean Carroll in his debate against William Lane Craig said, “It’s not hard to come up with ex post facto justifications for why God would’ve done it that way. Why is it not hard? Because theism is not well defined.”
A couple of days ago, Christian blogger John Mark Reynolds wrote about a time when life was discouraging. After prayer, he saw a rainbow over his house. He said, “Was it chance? It was not. It was God. Would that convince an atheist? Of course it would not, but then it was not a sign for the atheist. God was speaking through nature to me.”
Nope. If it wouldn’t convince an atheist, it shouldn’t convince you. If evidence were important, this being nothing more than a nice coincidence according to anyone outside your religion is the clue that you’ve deluded yourself. And that you dismiss that and embrace your interpretation as reality makes clear that you don’t care about evidence to support your belief.
This is the sign of an invented worldview.

Science doesn’t know everything.
Religion doesn’t know anything.
— Aron Ra

Image credit: Christine Schmidt, flickr, CC