The quick version
The short, doorstep comment is that the EU matters because of the peace and the stability, the opportunities and possibilities it brings.
The longer version…
The European Union matters enormously. It has been the context of British political and economic life for decades. It’s tended to under-state its contribution, so people are often not aware of how many development projects or pieces of investment begin in the EU. The contribution has been so great that we can take it for granted — and sometimes rail against its supposed shortcomings without bothering to look at the whole picture. The referendum changes this. Suddenly it might not be there. This posting is not about whipping up fear, but is about expressing some of the richness in which it is rooted, and the contribution it brings.
Culture and history
Europe has a long and convoluted history. There’s an intertwined heritage of culture and religion. There have been centuries of Europeans trading with each other, fighting with each other, sharing cultural influence and sharing faith. Up close, it looks like a story of rivalry. At a distance it looks more like the squabbling of long-married couples, where the words shouldn’t obscure the depth of the connection.