启示录中的666有什么含意？

http://www.jw.org/zh-hans/%E5%9C%A3%E7%BB%8F%E4%B8%8E%E7%94%9F%E6%B4%BB/%E5%9C%A3%E7%BB%8F%E9%97%AE%E7%AD%94/666%E6%9C%89%E4%BB%80%E4%B9%88%E5%90%AB%E6%84%8F/