This referendum is about withdrawing from the EU. The EU is bound by a set of Treaties that clearly state they are devoted to "Ever closer union" and clearly have a content that is about union. If the UK does not participate in full union then, when the other countries of the EU achieve it, the UK will be entirely marginalised. We can either join the full political union or leave.
Some people reading this might be surprised. You probably thought the referendum was about migration or money. No, this referendum is about centuries to come. It is about times when migration problems and Euro crises are a memory.
The arguments about migration and money are shameless attempts to buy your vote. They are trying to distract you from the issue, like offering sweets to kids. The Remain supporters hope that you are so selfish that you will swap some imaginary benefit for yourself for the entire long-term future of a Nation.
Why isn't this clear? The EU is based on a diplomatic method where all negotiations take place on condition that the final destination of the negotiations is not discussed. Jean Monnet perfected the method and it is used by all pro-EU supporters.