I'm currently reading Peter Rollins' brilliant and incisive book "Insurrection". One of the primary ideas is that on the cross, Jesus lost everything including God himself, and that this experience of the loss of God is the central dynamic at the heart of Christianity.
That is, any religious person can believe in God. But a Christian who has gone through the crucifixion experience, who has lost all faith and all trust in God, has really and truly experienced what Jesus experienced, the consuming truth behind Christianity.