The immediate response of most Kiwis to the Christchurch slaughter will have been shock and incredulity. But as the full dimensions and implications of the outrage become clearer, we need to reach a longer-term understanding.
Yes, it is unthinkable that our peaceable country should have borne witness to such barbarity. It is hard to overstate the sheer inhuman callousness that could lead anyone to fire an automatic weapon into a crowd of unarmed people.
But, throwing up our hands in horror will not be enough. We must understand, on several levels, how it came about and why it was not stopped. We need to understand, first, what it was that prompted anyone, claiming to be part of human society, and our society, in particular, to commit such an atrocity.
We are, sadly, accustomed to events of this kind when the perpetrators seem to be motivated by what they see as the wishes or commands of their God. In those cases, there is at least - however misguidedly - some semblance of a reason for what would otherwise be a purposeless act of destruction.
What is at issue here, however, is not some misinterpreted instruction from a supernatural being but rather a distorted belief system - formed and designed by fellow-humans - which the alleged perpetrator seems to have created and adopted for themself.
What is remarkable about that belief system is that its well-springs are not religious fervour or a quest for salvation but anger and hate directed against our fellow-human beings - against acquaintances and neighbours and workmates, the people we live and work with every day - against, in other words, "us".
What is further remarkable is the shocking arrogance on the part of the misguided converts - to the point they believe their distorted perceptions entitle them to kill and maim those who were unwittingly the targets of their hate and anger.
We cannot afford to let ourselves off the hook by labelling behaviours such as these as "beyond comprehension". We need to ask ourselves how it is that someone living in our midst could so grievously misread our own society as to believe that an act of this sheer malevolence could somehow be supported. We cannot dismiss it as an aberration when the evidence suggests so clearly that these attitudes were allowed to take root in our own soil - and we don't escape that reality and responsibility by dismissing the alleged perpetrator as an Australian.
We must accept that the tragedy was the product of a home-grown sickness. Only then will we achieve a society that does not provide a potting mix for such poisonous growths.
We might also register the significance of a Donald Trump (identified by the alleged shooter as an inspiration for his views) in creating a climate in which such attitudes might prosper. A society where fear, anger and hatred are encouraged as responses to those of different ethnicity or religion cannot expect to live at peace with itself.
As well as identifying the underlying causes, we will also have to learn practical lessons about how similar calamities can be forestalled in future. There are clearly lessons of gun control (how did such guns pass into such hands?) and of intelligence (why did the warnings of what was afoot on social media not get taken seriously?) and concerning the role of the social media themselves in providing a transmission medium for such violent and dangerous views.
Terrorism comes in many guises and with various excuses. Whatever mask it wears, we must be clear that it - and the forces that produce it - will not be tolerated in any form. We do that best by just learning to be kind to each other.
• Bryan Gould is an ex-British MP and Waikato University vice-chancellor.