This man is suspected by the police to have killed at least 84 people yesterday, most of them teenagers attending a political camp. He seems to have spent at least an hour walking around the island, shooting one at a time until the police arrived. The police suspects the same man detonated a 500 kg bomb in central Oslo earlier the same day, demolishing government buildings and killing several.
According to today’s news coverage and his Facebook page, he opposed Islam, celebrated Christian conservative values, and drew inspiration from the crusades (Christianity’s holy war against Islam).
Does this mean he was motivated by religion? Maybe, maybe not. Most Christians prefer the Bible’s teachings of love rather than the Bible’s teachings of hate and genocide. (Yes, they’re both in there.)
Two things are perfectly clear:
1. The guy is a nutcase. No mentally healthy person would even think about committing such an act. So Christianity may not have been his main driving force.
2. There is no better idea than religion to legitimize utterly horrific acts such as this one. Try this as a thought example: My opinions are correct and my actions are moral because the creator of the Universe fully agrees with me and is on my side. Try to argue against that. It’s impossible, which is precisely the idea behind any religious opinion or act, whether good or bad. Inspired or not, he certainly doesn’t doubt that he had God’s permission to shoot those kids to death. So whether you’re already a nutcase or not, religion will help strengthen your convictions and tell you what you want to hear: you’re right, the others are wrong.
Throughout history there are innumerable examples of religion (usually Christianity and Islam) giving people a mandate from God to commit atrocious acts and inflict limitless pain on their fellow human beings.
Conclusion: If you’re not already a nutcase, religion will ensure your mind becomes properly poisoned.
Religion Poisons 
Where is the source for that quote did he actually say that?
Breivik clearly stated that he was motivated by Christianity and saw himself as a modern crusader, as expressed in his manifesto and during the court hearings. However, the sentence under #2 is not a quote, it was meant as a thought example by the author of this blog. Thanks for pointing out that this could be misinterpreted, now clarified and quotation marks removed.