Christopher Hitchens, perhaps the most famous atheist in the public sphere and best-selling author of the book God is Not Great: How Religions Poisons Everything, answers that question. Hitchens recently did an interview with Marilyn Sewell, who is the minister of one of the largest Unitarian churches in the United States. Here's a brief excerpt from the interview where Hitchens talks about the importance of the resurrection:

Sewell: The religion you cite in your book is a generally fundamentalist faith of various kinds. I’m a liberal Christian, and I don’t take the stories from the scripture literally. I don’t believe in the doctrine of atonement (that Jesus died for our sins, for example). Do you make any distinction between fundamentalist faith and liberal religion?

Hitchens: I would say that if you don’t believe that Jesus of Nazareth was the Christ and Messiah, and that he rose again from the dead and by his sacrifice our sins are forgiven, you’re really not in any meaningful sense a Christian.

Sewell: Let me go someplace else. When I was in seminary, I was particularly drawn to the work of theologian Paul Tillich. He shocked people by describing the traditional God—as you might, as a matter of fact—as “an invincible tyrant.” For Tillich, God is “the ground of being.” It’s his response to, say, Freud’s belief that religion is mere wish fulfillment and comes from humans’ fear of death. What do you think of Tillich’s concept of God?

Hitchens: I would classify that under the heading of Statements That Have No Meaning—At All. Christianity, remember, was really founded by Saint Paul, not by Jesus. Paul says, very clearly, that if it is not true that Jesus Christ rose from the dead, then we the Christians are of all people the most unhappy. If none of that’s true, and you seem to say it isn’t, I have no quarrel with you... If all Christians were like you, I wouldn’t have to write the book.

In 1 Corinthians 15, Paul claimed that the resurrection was at the very heart of what it means to be a Christian. Though sadly he has not believed it himself, apparently Christopher Hitchens agrees.

"If Christ has not been raised, your faith is futile and you are still in your sins." ~1 Corinthians 15:17