Since the threat of cyberterrorism appears to be never-ending, how is intelligence central to understanding this threat vector?

One certainly can not fight against or conquer something that one does not understand. Being able to gather intelligence against an enemy, such as a the concept of cyberterrorism, is crucial to being able to neutralize the enemy. As such, intelligence agencies must be able to understand the process of hacking, identity theft, shutting down websites, sending viruses, etc. Intelligence agencies, such as the National Security Agency, have programs specifically dedicated to understanding and thwarting threats to internet networks. The NSA runs 24/7 online surveillance for cybersecurity operations. These cybersecurity operations help identify vulnerabilities within networks, develop solutions to prevent attacks, neutralize threats, and deal with an acute or on-going attack. Through their gathering of intelligence on cybersecurity and cyberterrorism, the NSA is able to publish advisories and recommend best practices for cybersecurity professionals to thwart cyberterrorism.