Do you have to believe in God to be a moral person? No. Yet, I understand why some believe God’s existence necessary for our actions to be meaningful: if God doesn’t exist then a person killing another person is no more immoral than an eagle catching and devouring a salmon; however, this is fallacious reasoning, in that, while humans, eagles and salmon are all animals, they are not all equally endowed with a capacity for moral reasoning or decision-making. The eagle doesn’t kill gratuitously; it kills to survive. Human beings even acknowledge there are exceptions to their rules when it comes to morality—for instance, killing out of self-defense or stealing to feed their starving family—(again) to survive. Morality evolved alongside the physical evolution of the human brain to help us survive. For this reason many a secular-minded rabbi has observed of the Ten Commandments that they are a “survival guide” for a Bronze Age society. Thus, the roots, or basis, of morality are to be found in our genes, not in the clouds.
In the context of Christianity (and every other major religion except Buddhism), there exists this assumption one first has to be religious (and God must exist) to be moral; and there are plenty of examples of secular-minded thinkers accepting this premise as valid: in his Farewell Address, George Washington argues it isn’t possible for a people to possess a direction if it doesn’t first possess an anchor (e.g. God). Abraham Lincoln appealed to Providence (a synonym for God) to demonstrate why slavery was objectively evil and should end. By contrast the renowned Lutheran pastor and theologian Dietrich Bonhoeffer argued in his Letters and Papers from Prison that boiling either God or morality down into some sort of immovable, unquestionable anchor was no longer an option to us: he argued that in humankind’s infancy, before the advent of modern science, we could appeal to the wisdom of simply following rules for the sake of following them (to avoid divine punishment for breaking them).
However, in the 20th century, when Bonhoeffer was writing, and with all of our scientific advances and with recent contributions to theological scholarship, we had to grow up and start taking more personal responsibility for living in the world. In short just following a set of prescribed rules (like the Ten Commandments) did not make one moral; instead, this was a form of Pharisaical legalism which made avoiding offending God the basis of right action as opposed to acting rightly for the sake of doing so. Again, right or moral action stems not from a need to placate an angry God or Church but to act rightly for the sake of doing so. This doesn’t mean someone—a theist, atheist, or otherwise—won’t choose to act immorally. If we weren’t free to be immoral, or at least somewhat free to choose a particular course of action, then we could not say we are moral beings. My take away from Bonhoeffer is do not confuse legalism for morality; and this is precisely what theists do when they judge atheists for not following God and ipso facto possessing morality.
Washington and Lincoln’s logic is both useful and problematic; that is, while the existence of a standard does appear to be necessary to determine the rightness or wrongness of a particular act, that standard is ultimately a human invention not a divinely created one; moreover, for an action to be considered either moral or immoral it suffices one simply believes their actions are meaningful; and ultimately the culture one belongs to determines whether X is wrong or Y is right. You do not need to appeal to something external, like God, for an action or omission to be considered either moral or immoral. Specifically, theists believing in an invisible, unproven, untestable, mythical and metaphysical being called God does not magically endow their actions with moral authority while the atheist’s actions by comparison are simply nihilism incarnate. We know you do not need a God to be moral precisely because atheists, who dismiss God as mere superstition, demonstrably act morally every day doing common sense things like “treating others as they’d like to be treated.” The Golden Rule is the culmination and product of tens of thousands of years of human evolution; the human brain, as it were, is hardwired and uniquely suited for morality in the same sense we are hardwired for grammar and logic.
 I would argue, though, there’s really no need to appeal to Providence to demonstrate slavery is wrong: all I need to do is ask the slave a simple question like “Do you want to be a slave?” And if they respond by saying “no” the rightness or wrongness is determined—in the here and now—well-established outside of an appeal to metaphysics.
 Arguably, Blaise Pascal penned his nonsensical “wager” during humankind’s infancy by reducing faith down to an existential bet that hopefully would pay off.
 Bonhoeffer, Dietrich, Letters from Prison, pages 478-480.
 All theists, agnostics, and atheists, believe that what they do and believe is meaningful; the only true difference that exists between these three is: the agnostic stresses intellectual honesty while accepting certain questions are by their very nature unanswerable; atheists abandon any external justifications (outside of science, concrete experience, reason and logic) for their actions and seek to be consistent in their thinking; they choose to take personal responsibility for them. Theists appeal to the almighty unfalsifiable God for their morality sometimes patting themselves on the backs for being “good by proxy” while those poor lost atheists are doomed to eternal perdition for having the audacity to ask hard questions finding the answers wanting.